Abstract: OBJECTIVE To investigate the relationship between group B streptococcal infection and vaginal microecology and premature rupture of membranes and their effect on pregnancy outcome. METHODS A total of 80 cases of full-term premature rupture of membranes were selected as premature rupture of membranes group, and 80 cases of full-term non-premature rupture of membranes were taken as control group in the hospital from Jan. 2015 to Dec. 2016. Lower reproductive tract group B streptococcal infection and vaginal microecological results of the two groups were observed. RESULTS The rate of vagina pH value >4.5, group B streptococcal infection and microecological imbalance in premature rupture of membranes group were 58.75%, 17.50% and 85.00%, which were higher than 32.50%, 3.75% and 55.00% in control group(P＜0.05). There were no significant differences in vaginal cleanliness, vulvovaginal candidiasis vaginitis and bacterial vaginosis between the two groups. In the 80 patients with premature rupture of membranes, the incidence of chorioamnionitis, puerperal infection, fetal distress and neonatal pneumonia in group B streptococcus positive group were 35.71%, 35.71%, 42.86% and 28.57%, which were significantly higher than 6.06%, 7.58%, 7.58% and 4.55% in group B streptococcus negative group(P＜0.05). There were no significant differences in the incidence of chorioamnionitis, puerperal infection, fetal distress and neonatal pneumonia between the microecological imbalance group and the microecological normal group. CONCLUSION Group B streptococcal infection in pregnant women of full-term premature rupture of membranes can increase the incidence of chorioamnionitis, puerperal infection, fetal distress and neonatal pneumonia, and vaginal microecological disorders has little impact on pregnancy outcomes.