The natural resources ministry said that more geological tests would be done on the samples gathered by a Russian research ship earlier this year, but early results showed that the 1,240-mile Lomonosov ridge is part of Russia.
"Results of an analysis of the Earth's crust show that the structure of the underwater Lomonosov mountain chain is similar to the world's other continental shelves, and the ridge is therefore part of Russia's land mass," the ministry said.
The ministry said the samples came from an expedition that took place in May and June, and an expedition two years ago to another undersea formation, the Mendeleev ridge.
The rush to map out and stake claims to the Arctic has been fuelled by scientific estimates that suggest as much as 25% of the world's undiscovered oil and gas could be hidden in the Arctic seabed.
Growing evidence that global warming is shrinking the polar ice - opening up resources and new shipping lanes - has also added to the urgency.
Last month two Russian submarines planted a flag on the seabed, making a symbolic claim to a vast swath of undersea territory.
Other Arctic Circle nations responded swiftly and angrily.
Canada's prime minister vowed to increase the country's icebreaker fleet and build two new military facilities in the Arctic.
Denmark sent a team of scientists to find evidence that the Lomonosov ridge was attached to its territory of Greenland. A US Coast Guard icebreaker also set off last month for a research expedition.