Sergei Ivanenko, speaking at the 13th party congress in the Moscow Region, said: "Yabloko is going to run in the nationwide elections. Unification with the SPS is not on the agenda."
He said the two parties had different political programs and different strategies.
"There are things more important than the division of seats in the State Duma," he said.
At the congress, Yabloko announced that it was the first non-parliamentary party to meet the Federal Registration Service's criteria, in line with new laws on political parties.
Analysts have said unification is one solution to the current difficulties Russia's liberal parties are in. New regulations for next year's parliamentary elections have made it less likely that either Yabloko or the SPS will get any seats in the Duma.
In 2003, Yabloko won only four seats and the SPS three in Russia's 450-seat Duma, and all from single-mandate districts, as both parties won less than the 5% of the vote necessary to elect deputies from party lists.
