Abstract： Objective To investigate the clinical significance and level variation of serum CA125 in patients with endometriosis.Methods Serum CA125 level of 28 recurrent cases,76 endometriosis cases and 80 healthy cases were retrospectively analyzed.Results In 76 endometriosis cases,the level of serum CA125 of 42 cases was over 35 kU/L,the sensitivity was 55.2%,the sensitivity of stage Ⅲ-Ⅳ(64.8%) was obviously higher than that of stage Ⅰ-Ⅱ (45.6%);In 28 recurrent cases,the values of serum level CA125 of 20 cases were over 35 kU/L,the sensitivity was 71.4%,and the prediction ability of CA125 in stage Ⅲ-Ⅳ(93.7%) was obviously higher than that in stage Ⅰ-Ⅱ (41.6%).Conclusion Serum CA125 played an important role in the diagnosis and prediction of endometriosis.