Russia has agreed to help Venezuela develop a nuclear energy programme.
The deal follows the first visit to the South American country by a Russian president.
Dmitry Medvedev also agreed to work with Venezuela in oil projects and building ships in another sign of their growing alliance.
Medvedev’s visit is part of an effort to boost Moscow’s influence in the West amid increasing tensions with the United States.
A situation welcomed by Venezuela’s President Hugo Chavez, one of Washington’s most outspoken critics. He thanked Russia for helping to create what he called a “multipolar” world no longer dominated by the USA.
Medvedev’s trip also coincides with a joint Russia-Venezuelan military training exercise, Moscow’s first major naval deployment in the Caribbean since the Cold War.