This study is a prospective double blind randomized clinical trial. Vaginal and rectal GBS screening culture are carried out for all pregnant women at 35-37 weeks of gestation in our out-patient department. Subjects with vagina and rectum GBS colonization are invited to participate in our study after informed consent. A total of 200 pregnant women will participate in the study during the 12-months trial period. They are randomly assigned to one of the two groups. The study group is treated with two oral capsules of probiotics once daily (before sleeping) for 14 days, and the control group will take 2 capsules of placebos. Vaginal and rectal GBS culture is repeated for all participators 2 weeks later. All participators will treated according to GBS guideline by CDC in 2002 during laboring.