Objective To evaluate the effect of serum LH level on the day of superovulation start on the prolonged gonadotropin-releasing hormone ngonist therapy on the outcomes of in vitro fertilization and embryo transfer (IVF-ET) in patents with ovarian endometriomas. Methods 75 patients with ovarian en-dometriomas were treated by laparoscopic cystectomy or laparotomy cystectomy or ultrasound-mediated cysts puncture, and gonadotropin-releasing hormone agonist (GnRH-α) was given for 3 to 4 times every 28 days after the operation. Superovulation started after 14 ～ 84 days of the last injection. All the patients were di-vided into two groups according to the level of serum LH. Group A included 30 patients whose level of LH was less than 0. 5IU/L, and group B included 45 patients whose level of LH was over 0.5IU/L and less than 1.5IU/L. The outcomes of IVF-ET were evaluated. Results The total ampoules of Gn administration and the ampoules of hMG needed in group A[(32.28±7.7) ampoules, ( 12.0±8. 9) ampoules,]were sig-nificantly more than that in group B[( 25.84±7. 1 ) ampoules, ( 6. 19±7.4) ampoules, P < 0.05] . The successful embryo implantation rate in group A( 18. 1% ) was lower than group B(26. 7% ), and the differ-ence has statistical significance ( P <0. 05). Conclusion The low level of serum LH on the superovula-lion day on the prolonged gonadotropin-releasing hormone agonist protocol will increase the ampoules of Gn administration and decrease the successful embryo implantation rate of IVF-ET, thus LH should be a more important reference parameter of superovulation start.