Ukraine is to get rid of its stockpile of highly enriched uranium by the year 2012.
The decision by President Viktor Yanukovich was the first tangible result from the 47-nation summit in Washington aimed at preventing nuclear terrorism.
The move is designed to make it harder for groups such as al Qaeda to get hold of fissile material that could be used to make an atomic bomb.
Ukraine’s agreement sets a precedent that summit host President Barack Obama wants other countries to follow.
Both the US and Russia are leading by example.
President Dmitry Medvedev and Obama are to sign a deal to dispose of 34 tons of weapons-grade plutonium.
Although not officially on the agenda, Obama is also trying to get a united international response to Iran’s nuclear activities.
His drive for tougher sanctions gained momentum after China’s leader President Hu Jintao said his government would help craft a U.N. resolution.
The spirit of cooperation between Washington and Beijing is in marked contrast to the last few months when disagreements over Tibet and their countries’ fractious economic relations have prevailed.