Critics have called the Kremlin-backed party a bureaucratic structure composed mainly of people serving their own narrow interests. Party leaders, including its new head, Prime Minister Vladimir Putin, have pledged a purge of ranks and a strategy reform.
Boris Gryzlov, chairman of United Russia's supreme council and speaker of the State Duma, the lower house of parliament, said a membership inventory would help uncover uncommitted members in the nearly 2 million-strong party.
"The review will leave the devoted United Russia members," Gryzlov said, adding that 1-1.5% of members, or 20,000-30,000 people, could be expelled. He also said that some people had applied to join the party a long time ago and were not even aware that they were members.
He said the final figure could "shock" journalists.
Putin became head of United Russia, which has a two third majority in the State Duma, after stepping down as president in May. He has refused to become a member of the party.
