Abstract: Objective：To discuss the relationship between vaginal colonization of group B Streptococcus (GBS) and vaginal clearing degree, and the adverse pregnancy outcome. Methods：Totally 1 864 cases of pregnant women after 35 weeks taking regular prenatal and delivery in Department of Gynecology，Maternal and Child Health Hospital of Jiading District in Shanghai City from Jun. 2012 to Aug. 2014 were enrolled. The vaginal clearing degree and GBS was detected regularly. The GBS carrier rates were compared between the two groups of normal and abnormal vaginal clearing degree. The incidences of premature rupture of membranes, premature delivery and puerperal infection were observed in GBS positive and negative groups. Results：In the 1 864 cases, the GBS positive rate was 5.15% (96/1 864). In 1 057 cases of pregnant women with normal vaginal clearing degree, GBS positive rate was 3.60% (38/1 057). In the 807 cases with abnormal clearing degree, the GBS positive rate was 7.19% (58/807,P=0.001). The incidences of premature rupture of membranes and puerperal infection of pregnant women with GBS infection increased (P＜0.05), and the risk (odds ratio, OR) increased by 13.40 times, 2.20 times, respectively. Conclusions：GBS carrier rate of pregnant women with abnormal vaginal cleaning degree is higher. GBS infection had adverse effects on perinatal outcome. It suggests that GBS detection in the late pregnancy is necessary.