Abstract： Objective To investigate the relationship between maternal plasma high mobility groupbox1 (HMGB1) and premature rupture of membranes(PROM) by detecting the concentration of HMGB1 in pregnant women,and to explore the significance of HMGB1 in the diagnosis of chorioamnion itis inpregnant women with PPROM.Methods The serum HMGB1 concentrations were measured in 55 pregnant women with PPROM and 40 healthy pregnant wonen at same pregnant term.40 pregnant women with PROM at term and 40 healthy pregnant women at same pregnant term,and Hematoxylin Eosin (HE) staining of placenta were performed after delivery of PPROM and PROM at term cases to observe the pathological changes of membranes of placenta.Results The plasma levers of HMGB 1 in pregnant women with PPROM and PROM at term were significantly higher than those in control group(t = 10.15,9.92 ,P ＜ 0.01) ,however,there was no significant difference in the levers of HMGB1 between pregnant women with PPROM and pregnant women with PROM (t = 0.65,P ＞ 0.05).Furthermore there was significant difference in the levers of HMGB1 between PPROM group with chorioam nionitis(t =7.25,P ＜ 0.05).Conclusion The HMGB1 concentration in pregnant women with PPROM or PROM at term is increased,but its diagnostic value for chorioam nionitis in patients with PPROM needs to be researched further.