Abstract: OBJECTIVE To explore the influence of group B Streptococcus（GBS） infection on the imbalance of vaginal microecosystem, serum inflammatory factors and maternal and neonatal outcomes of pregnant women. METHODS Pregnant women in the middle and late pregnancy who underwent GBS testing of cervical secretions in the First Affiliated Hospital of Hainan Medical College from Jan 2019 to Jul 2020 were selected as the research subjects. Among which, a total of 102 pregnant women with positive results were included in the GBS-positive group, and 100 pregnant women with negative test results were included as GBS-negative group. The vaginal microecological colonies, serum inflammatory factors and clinical outcomes of pregnant women in different groups were compared. RESULTS GBS was sensitive to penicillins, cephalosporins, linezolid and vancomycin, azithromycin and clindamycin. The proportion of vaginal microecological imbalance in GBS-positive group was 39.21%, significantly higher than that in GBS-negative group（P＜0.05）. The levels of serum interleukin-6（IL-6）, procalcitonin（PCT） and high sensitivity C-reactive protein（hs-CRP） in GBS-positive group were significantly higher than those in GBS-negative group（P＜0.05）, and incidence of premature rupture of membranes, chorioamnionitis, fetal distress, premature delivery, neonatal asphyxia, neonatal infection and puerperal infection was significantly higher than that in GBS-negative group（P＜0.05）. CONCLUSION GBS infection aggravated gestational vaginal microecological disorders, increased levels of serum inflammatory factors and the risk of adverse pregnancy outcomes.