The author studied the effects of cyclophosphamide to the Dental pulps of Rabbits. Eighteen rabbits were used. The experimental rabbits were given an intramuscular injection of cyclophosphamide 50mg. per 1.5Kg. of body weight. In order to investigate effects of cyclophosphamide to the pulps of rabbits the control and experimental rabbits were sacrificed, on 1,3,5,7,10, and 14 days after injection of cyclophosphamide and made preparations for histopathologic findings. The results were as fallows. 1. In the early stage after injection of cyclophosphamide, retrcgrade degeneration of pulps such as infiltration of inflammatory cells, vacuolization, hyaline degeneration and reticular tissue atrophy in pulps were revealed. 2. The pulps were recovered from 10 to 14 days after injection of cyclophosphamide.