Purpose: This study was performed to investigate the effects of Keukhachukeo-Tang (KCT) on the development of experimentally-induced endometriosis in rats. Methods : Endometriosis was induced in rats by autotransplanting uterine tissue to the peritoneum and devided them into three groups: (1) sham-operated group (n=8), (2) surgically induced endometriosis and untreated control group (n =8), (3) surgically induced endometriosis and KCT treated group. KCT (1,200 mg/head) was orally administrated for 15 days after operation. Then we measured the body weight, the volumes of endometriotic implants. The weight (body, left uterus and ovaries) and concentrations of cytokines (MCP-1, TNF-${alpha}$, IL-l${eta}$) in serum and peritoneal fluid were also measured. Histopathology, immunohistochemistry for COX-2, and histochemistry for mast cells in transplanted uterine tissue were performed. Results : - The volumes(mm$^3$) of endometriotic implants in KCT-treated group (107${pm}$66) were significantly decreased (p<0.05) compared with control group (405${pm}$318). - The contents(pg/ml) of MCP-1 in peritoneal fluid in KCT-treated group (6,940${pm}$893) were significantly decreased (p<0.01) compared with control group (8,632${pm}$1,245). - The contents(pg/ml) of TNF-${alpha}$ in peritoneal fluid in KCT-treated group (847${pm}$330) were significantly decreased (p<0.05) compared with control group (1,245${pm}$362). - The percentages(%) of positive epithelial layers for COX-2 in KCT-treated group (31${pm}$10) were significantly decreased (p<0.01) compared with control group (50${pm}$8). - The numbers of mast cells in adjacent tissue of transplanted uterine tissue in KCT-treated group (69${pm}$18) were significantly decreased (p<0.01) compared with control group (109${pm}$30). - The numbers of mast cells in stroma of transplanted uterine tissue in KCT-treated group(16${pm}$5) were significantly decreased (p<0.01) compared with control group (26${pm}$8). - Histopathologically, proliferation of endometriotic epithelia and stroma, and infiltration of inflammatory cells in transplanted uterine tissue of KCT-treated group were weakly observed than those of control group. Conclusion : From the above results, Keukhachukeo-Tang (KCT) have inhibiting effects on the development of transplanted uterine tissue. And these effects are related to the decreased concentration of MCP-1 and TNF-${alpha}$, decreased expression of COX-2, and decreased infiltration of mast cells by administration of Keukhachukeo-Tang.