Abstract: After administrating DES (diethylstilbestrol) by subcutaneous injections for 7 days, the changes in the morphology, distribution and number of mast cells in adult hamster epididymis caput and caudal were studied by using modified toluidine blue (MTB) staining, and cytochemical subsets of mast cells were identified by alcian blue-safranin O (AB-S) staining. The relationship of the number of epididymis mast cells between the morphology changes of epididymis caudal during DES-treated were explored. The results showed: Epididymis mast cells were belong to connective mast cells (CTMC), which distributed in the capsule and interstitium of epididymis caput and caudal. Some mast cells localized nearby epididymis tubular, and degranule mast cells could be seen in the epididymis caput and caudal in DES-treated hamster. Although mast cells area have no obvious difference in both DES-treated and control groups, but the number of epididymis caudal mast cells were significant increased in DES-treated (P＜0.01), particularly in epididymis caudal.