Abstract: Seven male rhesus monkeys were used for the investigation of the histopathological changes of epididymides in the 2.5th and 3.5th years after intra-vasa deferens injection of high molecular polymer HFMC.Various dosages of HFMC(Hydrogel for male contraception)were given to the animals:30 mg per vas deferens for 1 animal,60 mg for 3 and 100 mg for 3.The light microscopic observation showed that there were slight local watery degeneration of epididymal epithelium,falling of some epithelial cells and expansion of lumen in some epididymal tubules in the 2.5th year following intra vas injection of HFMC but no obvious abnormality was found under light microscope in the 3.5th year.The main ultrastructure changes in the 2.5th year showed the swelling of mitochondria,slight vacuolar change of endoplasmic reticulum and damage of sperms in the epididymal tubles.The ultrastructure changes in the 3.5th year were similar to those in the 2.5th year.It is suggested that HFMC may directly or indirectly affect the epididymal structure and the epididymal enviroment due to its gradual release of H+ as well as its partial and temporary occlusion of vasa deferens.This may be one of the reasons for its male contraceptive action.However,it seems that pathological may be restored after HFMC is progressively dissolved and excereted.