The two nations have been developing closer ties
China and Russia have signed a treaty settling a long-running territorial dispute along their border.
The pact - signed in Beijing by the two countries' foreign ministers - marks the end of a dispute which has been going on for 40 years.
The area saw armed clashes between the two sides during the Cold War.
Correspondents say the deal is the latest sign of warmer ties developing between Russia - a big energy exporter - and China, a big energy consumer.
The border between China and Russia is 4,300 km (2,700 miles) long, and the latest treaty resolves a dispute over the eastern part of the border.
According to Chinese reports, Russia will return all of Yinlong island (known in Russian as Tarabarov) and half of Heixiazi island (Bolshoi Ussuriyasky) to China.
China and the former Soviet Union fought border wars over this part of the territory nearly 40 years ago - when a rift developed between the two communist nations over after ideology.
But since the end of the Cold War, the two countries have re-adjusted their relationship and co-operated on many strategic issues such as North Korea and Iran, according to the BBC China analyst Shirong Chen.
China needs energy from Russia to feed its fast-running economic engine, whereas Russia wants to share China's economic opportunities, our correspondent says.
In the first five months of 2008, bilateral trade grew by 60%, according to the Russian Foreign Minister Sergei Lavrov.
However, China still has outstanding border issues with Japan and South Korea to the east, Vietnam to the south, and India to the south-west.
It has trumpeted its treaty with Russia as a new approach to border disputes.
But analysts say that with energy reserves behind many of the territorial disputes, it will be many more years before China can hope to settle its borders with all its neighbours.