An epidemiologic study of perinatal colonization of group B streptococcus (GBS) was carried out. Six hundred mother-infant pairs were studied at Beijing Tiantan Hospital. Maternal carriage rate of GBS was 8% with a neonatal colonization rate of 6.7%. Overall perinatal carriage rate was 13%. Women with perinatal colonization showed prone to have more premature and low birth weight babies. We did not find that perinatal colonization was associated with prolonged rupture of membranes and IUGR in our study group. Serotypical study showed that most frequent GBS type isolated from the carriers was III, followed by I a. Antibiotic sensitivity study showed that more than half of the GBS strains were resistant to the antibiotics a severe problem which might have caused by abuse in this country.