Abstract： Objective To explore the changes of the frequency and cytokine production of CD19 + CD5 + B cells in Endometriosis before and after treatment.Methods Flow cytometry and quantitative PCR were used to assess the frequency,cytokine expression of CD19 + CD5 + B cells in the peripheral blood,peritoneal fluids and endometrium biopsies of 35 patients with Endometriosis and 29 patients with myoma of uterus (control subjects).Changes in the CD19+ CD5+ B cell compartment in the peripheral blood were compared before and after treatment.Results All 35 endometriosis patients had higher frequencies(all P ＜0.01 ) of CD19+ CD5 + B cells in the peripheral blood,peritoneal fluids and endometrium biopsies [ (13.1 ± 1.9)％,(12.1 ±2.0)％,(11.7 ± 1.7)％] than 29 control subjects[ (2.9 ±0.8)％,(2.6 ±0.9)％,(2.8 ±1.1 )％ ].CD19 + CD5+ B cells from endometriosis patients expressed higher IFN-γ[ (7.2 ± 1.0) × 103,(7.9±1.3) ×103,(7.4±1.1) ×103 copies] than control subjects [ (1.9±0.7) ×103,(2.2±0.8) ×103,(2.0 ±0.5) × 103 copies).The endometriosis patients also had higher IL-10 production of CD19 + CD5 + B cells [ (6.4 ±0.9) × 103,(6.8 ± 1.2) × 103,(6.1 ±0.8) × 103 copies] than control subjects [ ( 1.7 ±0.5) × 103,(2.1 ±0.9) × 103,( 1.6 ±0.4) × 103 copies].Compared with control subjects,the endometriosis patients had a clinical response to treatment demomtrated a significant decrease in CD19 + CD5 + B cells in the peripheral blood[ ( 13.1 ± 1.9)％ vs (7.3 ± 1.2)％ ],expressed lower IFN-γ [ (7.2 ± 1.0)×103 copies vs (3.3 ±0.6) × 103 copies],produced less IL-10 [(6.4 ±0.9) × 103 copies vs (3.2 ±0.7) × 103 copies].Conclusions CD19+ CD5 + B cells might play an important role in the pathogenesis of endometriosis through higher IFN-γand IL-10 expression.