On the Czech route, you do not have to prove that your ancestor was a citizen. You have to prove when and how he or she ceased to be one, and that is a historical and legal question with a definite answer for most American families. This guide explains the laws and the treaty that governed the loss of Czechoslovak citizenship and the documents that prove it. This guide reflects official pages we checked in October 2026. Rules, fees, forms and waiting times change and differ between embassies, so confirm every detail with the embassy or consulate that will receive your application.
Why the Czech route asks for proof of loss
Section 31 of Act No. 186/2013 lets people who lost Czech or Czechoslovak citizenship, and their children and grandchildren, acquire it by declaration. The Ottawa embassy therefore asks for a document that certifies the date and the basis on which the parent or grandparent ceased to be a citizen, such as an original foreign citizenship certificate or an original Czechoslovak release certificate. See our Czech declaration guide.
Citizenship laws by period
| Period | Law | Notes |
|---|---|---|
| 28 October 1918 to 30 September 1949 | Act No. 236/1920 | Citizenship by birth was determined by the citizenship of the father |
| 1 October 1949 to 31 December 1968 | Act No. 194/1949 | A child born abroad became a Czechoslovak citizen if both parents were Czechoslovak citizens |
| From 1969 | Separate Czech and Slovak republic citizenships were instituted | Some people born abroad to Czechoslovak citizens never acquired citizenship of either republic |
| 1993 | Separate states | Czechoslovakia split on 1 January 1993 |
In the Slovak part of the country, a Hungarian statute of 1879 on the acquisition and loss of Hungarian state citizenship remained in effect even in Czechoslovakia until 1949, according to a Slovak law firm’s history of citizenship law. See our regions guide.
The US treaty
- Dates. An agreement between Czechoslovakia and the United States on prevention of dual citizenship was in force from 14 November 1929 until 20 August 1997, and was suspended between 17 September 1938 and 7 May 1957, when either country was in a state of war, according to the Czech embassy.
- Effect. It prevented dual citizenship of Czechoslovak citizens who became naturalized in the United States, and of US citizens who became naturalized in Czechoslovakia.
- One-sided in practice. Migration Online notes that the United States did not comply with the treaty, so Czechoslovak citizens who became US citizens lost their Czechoslovak citizenship, while US citizens naturalized in Czechoslovakia kept their US citizenship.
- Age. Wikipedia notes that loss applied to a person naturalized in the United States at age 21 or older, or to a minor child whose US citizenship derived from parents who naturalized.
The US Helsinki Commission wrote that approximately 30,000 Czechoslovak emigrés who sought refuge in the United States during and after the Second World War automatically lost their citizenship under the treaty when they became US citizens. This is why the Czech declaration mainly concerns Americans with Czech ancestry: a US naturalization certificate documents loss.
Other ways to lose citizenship
- Release. A person could be released from the state bond at his or her request, documented by a Czechoslovak release certificate (propuštění ze státního svazku).
- Naturalization in another country. Wikipedia says that before 1993, simply naturalizing in another country did not automatically mean loss unless the person was 21 or older and naturalized in the United States, and that Czechoslovakia had no similar treaty with any other country. If your ancestor naturalized in a country other than the United States, you may need to prove loss by other means.
- Other agreements. Agreements preventing dual citizenship with the Soviet Union, Hungary and Poland were also in effect in 1949 to 1968, according to the Czech embassy’s guide.
- Decrees and treaties after 1945. Some losses fall under the exclusions, such as the decree on persons of German or Hungarian nationality. See our Czech guide.
The 1999 law
Act No. 194/1999 allowed some former Czechoslovak citizens to acquire Czech citizenship, according to Migration Online, which notes that Czech Americans had not been able to obtain citizenship because they had lost it by release or under the treaty. The Helsinki Commission welcomed the 1999 provisions as ending the ban on dual citizenship for Czech Americans. The later route under Section 31 was added with the 2019 amendment, according to the Los Angeles consulate.
What the Slovak route asks instead
The Slovak route does not ask you to prove that your ancestor lost citizenship. It asks you to prove that the ancestor was a Czechoslovak citizen born in the territory of present-day Slovakia. See our Slovak guide.
Documents that prove loss
- A US naturalization certificate, original, apostilled and translated into Czech where required.
- A Czechoslovak release certificate.
- A foreign citizenship certificate for a country other than the US, together with evidence of how Czechoslovak citizenship was lost.
- Official records from the Czech archives, which the embassy can help you request.
A routine for proving loss
- Identify the parent or grandparent and the year he or she became a citizen elsewhere.
- Find the naturalization certificate or the release certificate. See our emigration guide.
- Check the age and the date against the treaty’s periods.
- Note any gaps, such as a minor child or a wartime suspension.
- Ask the embassy how to document loss if your ancestor did not naturalize in the US.
Illustrative composite (not a real family): A reader’s grandfather naturalized in the United States in 1946, which falls in the period when the treaty was suspended, from 17 September 1938 to 7 May 1957. She does not assume that this means he kept his citizenship. She asks the embassy how the Czech authorities treat a naturalization in that period, because the answer is a legal question for them to decide.
Common mistakes
- Assuming naturalization in any country ended citizenship. The treaty was with the United States.
- Ignoring the suspension period. The treaty did not apply from 1938 to 1957.
- Forgetting the age rule. Age 21 or older mattered.
- Skipping the certificate. The Czech embassy asks for the document certifying loss.
- Treating this as legal advice. Ask the embassy or a lawyer.
Continue with the complete guide and our guide to choosing a route, and browse Czech & Slovak Citizenship by Descent. Sources: the Czech embassy’s guide to Czech citizenship in 1918 to 1949, its guide to citizenship in 1949 to 1968, Migration Online on Act No. 194/1999, the U.S. Helsinki Commission, Wikipedia on Czech nationality law and a Slovak law firm’s history of citizenship law.
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