Objective: This study aimed to evaluate the therapeutic efficiency of tibolone in an experimental rat model of intra-abdominal endometriosis. Material and Methods: In this experimental study, intra-abdominal endometriosis was induced in 30 female rats surgically. Four weeks after this procedure, laparotomy was performed again. The dimensions of the endometriosis foci were recorded and right after, the operation was completed. Rats were randomly divided into three groups and subsequently, the treatment was started. In the first group (n=8), a single dose of 1 cc 0.9% NaCl was injected subcutaneously. In the second group (n=8), intramuscular injection of 1 mg leuprolid acetate was administered. In the third group (n=8), 1 mg/kg/day of tibolone was given by gavage. At the end of 4- weeks of drug administration, laparotomy was performed to all rats. The dimensions of the endometriosis foci were recorded. Afterwards, all the rats were sacrificed. The differences in the areas of endometriotic implants and adhesion scores were compared between the groups. Results: The dimensions of the endometriosis foci in the groups treated with leuprolid (p<0.05) and tibolone (p<0.05) were significantly diminished compared to that of the control group. No statistically significant differences were found between the treatment groups. Conclusion: In a rat endometriosis model, tibolone has a similar efficiency as that of leuprolid acetate, an agent used for conventional medical treatment of endometriosis. With its androgenic and progestagenic characteristics, tibolone deserves attention as an alternative agent in the medical treatment of endometriosis in human.