In this study, effects of cyclophosphamide on the growth of the mandibular condyle head were investigated with Spraque-Dawley rats of the 28 days of age. Rats were devided into four groups. Three were used as experimental groups, and one as control. Each rat in experimental group was injected intraperitoneally with cyclophosphamide repeatedly three times, 20mg/kg for the first group, 40mg/kg for the second, and 60mg/kg for the third each time. Rats in control group were injected with physiological salime in the same method. Rate in each group were sacrificed at 5, 10, and 15 days following the 1ast injection. The specimens were stained with H-E, toluidine blue, PAS, and alcian blue. The results were as follows; 1. In experimental group, with increasing the injection doses, the thickness of the condylar cartilage from the transitional zone to the hypertrophic zone became thinner in control group. 2. Weaker metachromasia to toluidine blue and less positive reaction to PAS were seen. 3. In promary marrow cavity the fewer trabecular was formed, the direction of trabecular formation became obscuerer, and the lower density of bone was resulted in.