The present invention is directed to two new polymorph Form V and Form F of desvenlafaxine succinate, to processes of their preparations, pharmaceutical composition comprising such materials and their use in therapy. Form V is prepared from recrystallizing desvenlafaxine succinate in a mixture of tetrahydrofuran and ethanol. Form F is obtained from recrystallization of desvenlafaxine succinate in a mixture of cyclohexane and polar solvents such as ethanol, THF, methanol or isopropyl alcohol.