The law of Ukraine does not allow dual citizenship. If a person is a citizen of any state other than Ukraine, he automatically loses Ukrainian citizenship (Article 19 of the Law of Ukraine "On Citizenship"). A man who has the citizenship of Ukraine and one more, of another country, is considered a citizen of Ukraine. Therefore, the procedure for crossing the border must be decided taking into account other reasons.
Men who have the citizenship of another country at the same time as the citizenship of Ukraine can cross the border with a non-Ukrainian passport. Customs control cannot track the presence of a second passport.