Abstract: Objective To analyze the effect of group B Streptococcus (GBS) colonization on pregnancy outcome and neonatal infection.Methods 3554 pregnant women who delivered in our hospital from September 1, 2016 to August 31, 2017 and underwent GBS screening in the third trimester of pregnancy were divided into GBS colonization group (241 cases) and non-GBS colonization group (3313 cases) according to the screening results. Age, cesarean section rate, abnormal pregnancy history, antenatal fever, incidence and prognosis of neonatal infection in the two groups were analyzed retrospectively.Results ①Compared with the non-GBS colonization group, the pregnant women of GBS colonization group were older (29.3 vs 28.6, P=0.048), with more abnormal pregnancy history (including spontaneous abortion, ectopic pregnancy, induced abortion due to fetal malformation, stillbirth) (10.0% vs 3.9%, P=0.000), higher incidence of prenatal fever (2.1% vs 0.3%, P=0.002), premature rupture of membranes (27.8% vs 21.0%, P=0.015), and chorioamniotic meningitis (19.5% vs 14.7%, P=0.05). Preventive treatment with intrapartum antibiotics prophylaxis (IAP) (15.8% vs 6.8%, P=0.000) was more frequently used in GBS colonization group than non-GBS colonization group. ② The incidence of neonatal sepsis in GBS colonization group was higher than that in non-GBS colonization group (2.5% vs 0.8%, P=0.025). GBS was detected in 2 neonatal blood cultures. One of the 2 neonates also detected GBS in gastric juice. The incidence of neonatal pneumonia was higher (4. 1% vs 1.4%, P=0.005), and the incidence of neonatal asphyxia was higher (3.3% vs 1.4%). There was one neonate with purulent meningitis in GBS colonization group,. Both of their blood culture and cerebrospinal fluid culture were Escherichia coli. They were cured and discharged after anti-infection treatment. There was no case of purulent meningitis in non-GBS colonization group. There was no difference in the incidence of neonatal conjunctivitis between the two groups. The incidence of pathogenic bacteria infection in neonates with GBS colonization was significantly higher than that without GBS colonization.Conclusion GBS colonization in the third trimester can increase the risk of adverse pregnancy outcomes, leading to an increase in neonatal GBS infection rate, and clinical should be vigilant.