This experimental study was made to investigate the effect of the "Hi-Pol" composite resin on the human dental pulp. 38 cavities of healthy permanent teeth were divided into 5 groups which were used as experimental materials. Group 1: Zinc Oxide-Euginol paste was applied to the cavities as controls $cdots;cdots8$ cases Group 2: "Hi-Pol"*filling with Dycal** base $cdots;cdots9$ cases Group 3: "Hi-Pol" filling without Dycal base $cdots;cdots9$ cases Groud 4: Adaptic*** filling with Dycal base $cdots;cdots6$ cases Group 5: Adaptic filling without Dycal base $cdots;cdots6$ cases The treated teeth were extracted after 1 week, 2 weeks, 3 weeks and 4 weeks and processed for histological study. The results obtained from this experimental study were as follows; 1. The controls applied zinc oxide-eugenol showed the minimal pulp response and group 3 and group 5 showed the most severe pulp response. 2. In group 3 and group 5, the severity of pulp response increased in intensity according to the time elapsed. 3. In group 2 and group 4, the mild pulp response was found in earlier stage and the repairing process could be observed in later stage. * Boo-Pyung Co., Korea ** L. D. Caulk Co., Milford, Del. 19963 *** Johnson and Johnson Co., New Brunswick, NJ 08903.