He was 81.
He breathed his last at Ram Manohar Lohia Institute of Medical Sciences here, party spokesperson said.
SP supremo Mulayam Singh Yadav and Uttar Pradesh Chief Minister Akhilesh Yadav expressed profound grief over the demise of the MLA, an official release said.
Praying for peace of the departed soul, they expressed their deep sympathies to the family members.
In his condolence message, the Chief Minister said throughout his life, Mitrasen Yadav struggled for the cause of socially and economically backward and down-trodden people.
Mitrasen Yadav was elected to state Assembly for the first time in 1977. He was a five-time MLA and three time Member of Parliament.