Objective:To investigate the influence of group B streptococcus(GBS)infection on vaginal microecology and preg-nancy outcomes in late pregnancy.Methods:Retrospective study on clinical data of late pregnant women who received prenatal vaginal secretion examination were selected for the study.According to the GBS infection detection results,they were divided into GBS positive group(n=71)and GBS negative group(n=49).The vaginal microecological imbalance,vaginal cleanliness grading,delivery modes of pregnant women,adverse pregnancy outcomes of pregnant women and perinatal infants were compared between groups.Results:The incidence rate of bacterial vaginosis(BV),vaginal microecological imbalance rate and proportion of patients with vaginal pH value＞4.6 in GBS positive group were higher than those in GBS negative group(P＜0.05).The proportion of patients with vaginal cleanliness grade 1 in GBS positive group was lower than that in GBS negative group(P＜0.05)while the proportions of patients with grade 3 and grade 4 were higher(P＜0.05).The rate of natural vaginal delivery in GBS positive group was lower(P＜0.05)while the rate of con-version to cesarean section was higher compared with that in GBS negative group(P＜0.05).The incidence rates of adverse pregnancy outcomes of pregnant women(intrauterine infection,premature rupture of membranes,amniotic fluid turbidity/pollution and puerperal infection)and perinatal adverse outcomes(premature birth,low birth weight,pneumonia,GBS infection)were higher in GBS positive group than those in GBS negative group(P＜0.05).Conclusion:GBS infection has a certain impact on vaginal microecological balance and vaginal cleanliness in late pregnancy,which can increase the risk of adverse pregnancy outcomes and perinatal adverse outcomes.