"Lathar has been expelled from the place of president SP Yuvjan Sabha with immediate effect," SP spokesman and MP Ramgopal Yadav said in a release issued here.
Lathar was not taking interest in party works and some other serious allegations were there against him, Yadav said.
During the by-election from Mant seat in June, vacated by RLD leader Jayant Chowdhury, Lahar was fielded as a party candidate.
He was considered close to Chief Minister Akhilesh Yadav.