Objective     To investigate the effects of cyclophosphamide (CTX) on proliferation and morphology of human alveolar rhabdomyosarcoma cell-line PLA-802 xenografted tumor in nude mice.       Methods     Sixteen nude mice which had been implanted PLA-802 by subcutaneous injection into the right armpit were divided into control group (5 mice)

normal saline group (5 mice) and 20 mg/kg CTX group (6 mice). They were given CTX or normal saline intraperitoneally once every two days

starting on the 7

th

day after tumor cell transplantation. Tumor volumes were measured every two days for drawing

the growth curve. Animals were anesthetized on the 26

th

day after tumor cell transplantation to get weight and specimens of the tumors. Specimens were stained of HE or EM

and then examined with light microscope and electron microscope.        Results     The proliferation of xenografted tumors was inhibited significantly (P0.05). The inhibition rate of the tumors was 85.55%. The morphology of xenografted tumor was changed after CTX treatment. It appeared that neoplastic cells arranged in alveolar form

which were comparted by fibrous tissue and were of fewer blood vessels. Neoplastic cells were oval

racket-shape or short fusiform

and nucleus were oval or round-like in various sizes. Karyokinesis was less. There were various amount of myofilament

even muscle myofibril in cytoplasm.        Conclusion     CTX can inhibit the proliferation and change the morphology of PLA-802 xenografted tumor.