A dispute between Russia and Ukraine in January cut supplies to Europe
Ukraine has said it has settled an outstanding gas bill with Russia, calming fears Europe may suffer any further disruptions to gas supplies.
Prime Minister Yulia Tymoshenko blamed President Viktor Yushchenko for blocking payment, causing the delay.
Last week, Russian Prime Minister Vladimir Putin raised concerns that Ukraine had not paid for its gas.
In January, many countries in Europe were left short of gas due to a payment dispute between Moscow and Kiev.
"Today we paid Russia the next $500m (£301m)," said a statement from the Ukrainian prime minister's office.
It added that the payment had been "extremely difficult".
Mrs Tymoshenko has blamed Mr Yushchenko for blocking payments from Ukraine's central bank to the Russian gas giant Gazprom.
The two central political figures in Ukraine are standing against each other in next year's presidential elections.
Russia provides about a quarter of the gas consumed in the EU and 80% of that is piped through Ukraine.