Objective To investigate the expression of high mobility group protein box1 (HMGB1)in ovarian endometriosis tissue and to provide new idea for early diagnosis,treatment and prognosis of endometriosis.Methods The levels of HMGB1 in ectopic endometrium and eutopic endometrium of 69 patients with ovarian endometriosis and endometrium of 69 cases with non-endometrioses were detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western-blotting.Results HMGB1 was expressed in all the three groups (ectopic endometrium eutopic endometrium endometrium with non-endometrioses).The relative expression level of HMGB1 mRNA was 0.54383 ± 0.0565,0.3016 ± 0.0614,and 0.1536 ±0.0444,respectively (F =377.923,P ＜ 0.0001).The relative of HMGB1 protein was 0.83990 ±0.12869,0.40100 ±0.16425,and 0.19986 ± 0.08162,respectively (F =185.625,P =0.0000).The expression level of HMGB1 was related to clinical stages (t =10.28,P ＜0.01) ; however,it was not obviously related to age,the diameter of lump,and course of disease (P ＞ 0.05).Conclusions Over expression of HMGB1 in ovary endometriosis indicates that HMGB1 plays a significant role in occurrence and development of ovary endometriosis.The expression of HMGB1 in endometriosis eutopic endometrium was much higher than that of non-endometrioses endometrium,which supports the eutopic endometrium determinism.The overexpression of HMGB1 was consistent with clinical stage,which proves that HMGB1 maybe be tightly associated with the severity of the disease and to likely become biomarker.