Ukrainian state energy firm Naftogaz says it has transferred $1.65 billion to Russia's Gazprom, the second tranche of a debt repayment.
In October, Moscow, Kyiv, and the European Union reached a deal under which Russia would restart flows to Ukraine over the winter in return for Ukraine paying $3.1 billion in two tranches by the end of the 2014.
The first tranche of $1.45 billion was transferred in early November.
Russia started pumping gas to Ukraine in December after Kyiv transferred a prepayment of $378 million to state-controlled Russian gas company Gazprom for gas shipments in December.
Russia wants Ukraine to pay for gas in advance.
Russian gas supplies to Ukraine were halted six months ago due to a dispute over prices and unpaid debts.