To observe the effect of Heulbuchuketang on endometriosis, surgically induced endometriosis in rats was treated with Heulbuchuketang for l00days. The result are as follows: 1. Fragments of right uterine horn were implanted at the serosal wall of small intestine and its adjacent aterial suppling branch. After 4 weeks later endometriosis was observed at the area of implantation of small intestine. 2. After l00-day-treatment, the size of the endometriosis of treated group was much smaller compared to those of the untreated group. Especially the result of the later 60-day-treatment was much better than that of the early 40-day-treatment. 3. In case of inflammation or pustula induced from endometriosis, the size of abnormal endometriosis tissue showed no change after the total treatment and fibrotic change was often founded there, which was not responding to Heulbuchuketang. 4. In the ovary of untreated group, primordial follicle, primary follicle, maturing primary follicle were easily founded and there was no difference in shape and size between the ovary of Heulbuchuketang treated group. From the upper 1 to 4 laboratory result it can be suggested that Heulbuchuketang can be specially effective to mild endometriosis with conservating the ability of fertility.