A poll by voters after leaving the polling stations showed that comedian Volodymyr Zelinsky won an overwhelming victory in the second round of the Ukrainian presidential election.
The poll showed Zelinsky had a support rating of more than 70 percent. He qualified in the first round of elections held three weeks ago against 39 candidates.
Zielinski has battled veteran President Pietro Poroshenko.
Boroshenko admitted defeat, but said in a speech to his supporters gathered in the capital Kiev that he will not retire from the political arena.
The Ukrainian president has great powers related to security, defense and foreign policy of the country.
"I promise I will not let you down," Zelinsky told his supporters.
"Although I am not officially an official president yet, as a Ukrainian citizen, I can tell all the post-Soviet countries: Look at us, everything is possible."