Objective Methods 28 male Mongolian gerbils were divided into 4 groups，7 per group． Set a negative control group，three CP groups ( low-dose group，medium-dose group and high-dose group) ． Cyclophosphamide was given to the CP groups by intraperitoneal injection for 5 days． 30 days after the giving drugs，we anaesthetized the gerbils，opened their abdomen and took out their two testicles． Then we made smears with the sperm suspension，and air dried them，and then fixed them with methanol for 10 minutes，and then air dry them again． After the above steps，we stained them with 2% eosin for 30 minutes，then we rinsed them with distilled water，and dry them for film-reading observations． The observation was about the influence of cyclophosphamide on the Mongolian gerbils' sperm． Results Compared with the negative control group，the rate of sperms abnormalities in the three CP groups showed great difference． The rate in the low-dose group and the medium-dose group was obvious different from the rate in the high-dose group( P＜0. 01 ) ． The rate in the low-dose group showed little difference from the rate in the medium-dose group( P＞0. 05) ． Morphological observation showed that:the abnormal effect of cyclophosphamide on gerbils' sperms included tail folding，tail weight / length / distortion and no hook． Conclusions Cyclophosphamide has a certain teratogenic rate on Mongolian gerbils' sperms． And it influenced their tails most． In a certain dose range，the rate of abnormalities showed little difference，while when the dose was higher than a certain level，the rate of abnormalities rose together with the dose of cyclophosphamide rose．