Travel to Ukraine
ENTRY / EXIT REQUIREMENTS FOR U.S. CITIZENS: You need a valid passport to enter Ukraine. If you are a U.S. citizen, you do not need to have a Ukrainian visa as long as you will be in Ukraine for fewer than 90 days within a 180-day period. You need a visa or valid Ukrainian residency permit for all stays longer than 90 days. You cannot get a Ukrainian visa at the airport or at the border. If you need a visa, please get it in advance at a Ukrainian Embassy or Consulate. Contact information for Ukrainian Embassies and Consulates outside of the United States is available on the Ukrainian Ministry of Foreign Affairs website. [1]
google: USA and Ukraine citizenship, how to travel with two passports when duel citizenship isn't allowed by Ukraine?