Abstract： Objective To compare clinical effect of gonadotropin releasing hormone agonist(GnRH-a) alone and GnRH-a combined with low-dose dydrogesteronea and estradiol valerate on sex hormone, hypoestrogenic symptoms, quality of life and bone mineral density (BMD)in treatment of endometriosis.Methods Seventy patients with moderate or severe endometriosis, who were diagnosed by laparotomy or laparoscopic surgery within two months, were randomly assigned into two groups.35 patients in GnRH-a group were treated by goserelin (3.6 mg)for three months, and 35 patients in add-back group were treated by goserelin (3.6 mg)combined with estradiol valerate 0.5 mg and dydrogesteronea 5 mg daily.Before and after the treatment, clinical parameters were recorded and analyzed, including visual analog scale (VAS), medical outcomes survey short form 36 (SF-36), Kupperman menopausal index(KMI), BMD, the serum level of follicle stimulating hormone (FSH), estradiol (E_2) and bone gla-protein (BGP) .The first menstruation and VAS were also followed up after treatment.Results Every 3 cases in two groups lost follow-up.(1)Reproductive hormone: the level of E_2 in add-back group [(94 ± 71) pmol/L]was significantly higher than (54±52) pmol/L in GnRH-a group(P <0.01).The level of FSH in add-back group [(3.0 ± 1.9) U/L]was significantly lower than (5.7 ± 2.9) U/L in GnRH-a group (P < 0.05).(2) VAS: after treatment, VAS in both group decreased significantly when compared with that before treatment(P < 0.05), and remained until menstruated.(3) KMI: KMI in add back-group (10 ± 8) was significantly lower than (14 ± 6) in GnRH-a group (P < 0.05).(4) BMD: compared with that before treatment, BMD decreased significantly after treatment in GnRH-a group (P < 0.05), no remarkable difference of BMD was observed before and after treatment in add-back group.Before treatment, serum BGP in both groups did not show statistical difference.After treatment, the level of BGP in GnRH-a group [(7932±5206) ng/L]was significantly higher than (5419±2917) ng/L in add-back group (P <0.05).Conclusions GnRH-a combined with estrogen-progesterone regimen could relieve pain from endometriosis as effectively as GnRH-a alone and reduce hypoestrogenic symptoms and bone loss.Therefore,it is a safe and effective treatment.