The Ukrainian parliament renounced Ukraine's "non-aligned" status to work towards Nato membership, angering Moscow, which views Nato's eastward expansion as a threat to its own security.
Accession to the military alliance is likely to take years, but a Nato spokesman in Brussels said: "Our door is open and Ukraine will become a member of Nato if it so requests and fulfils the standards and adheres to the necessary principles."
Russia called the vote "an unfriendly step towards us".
"This political vector will only add to nuisances and acuteness in ties," said Andrei Kelin, Russia's envoy to the Organisation for Security and Cooperation in Europe.
Addressing deputies in Kiev before the vote, Ukrainian foreign minister Pavlo Klimkin said scrapping Ukraine's neutral status underscored its determination to pivot towards Europe and the West.
“This will lead to integration in the European and the Euro-Atlantic space,” Mr Klimkin said.
The amendment passed easily, receiving 303 votes, 77 more than the minimum required to pass into law.
Ties between Moscow and Kiev are at an all time low since Russia's annexation of the Crimean peninsula from Ukraine in March and a pro-Russian separatist rebellion in eastern Ukraine.
The pro-Western authorities in Kiev accuse Russia of orchestrating and arming the uprising in the east after the overthrow of a Ukrainian president sympathetic to Moscow. The Kremlin denies that it is behind the revolt.
Russian foreign minister Sergei Lavrov said Ukraine's renunciation of its "non-aligned" status was counterproductive and would only boost tensions around the crisis in eastern Ukraine.
“It is counterproductive. It will only escalate the confrontation and creates the illusion that it is possible to resolve Ukraine’s deep internal crisis by passing such laws,” Tass news agency cited Lavrov as saying.
Reuters