Gazprom CEO Alexei Miller said supplies, which were suspended in the spring, recommenced earlier after the company received USD 234 million out of a promised USD 500 million prepayment from Kiev.
The deal, which was signed last month with the help of the European Union, will ensure that Ukraine will receive Russian gas for six months through March 2016.
Past gas disputes between Russia and Ukraine have led to cutoffs of supply. One standoff in 2009 caused serious disruptions in shipments EU countries in the dead of winter.
Last winter, Russia and Ukraine struck an emergency deal on gas prices, but that expired.
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EU-sponsored talks seeking a similar accord for the coming winter began in March. Under the deal, Russia lowered the price it charged Ukraine to the same level granted to neighboring countries, from USD 251 per 1,000 cubic meters to about USD 230.
The European Commission has pledged at least USD 500 million of aid to Ukraine for the gas supplies.