The Labour Party lost about 91,000 members last year, according its accounts.
The party had 432,213 members at the end of 2021, down from 523,332 in 2020.
Leader Sir Keir Starmer said party membership always declines between elections - but left-wing critics said Jeremy Corbyn's departure had sparked an "exodus" of members.
Labour is still thought to have more than twice as many members as the Conservative Party.
The Conservatives do not publish membership figures, but the party recently indicated that it was more than 160,000.
https://www.bbc.co.uk/news/uk-politics-62582014