Group B Streptococcus (GBS) is a major cause of severe systemic and local infections in newborns. This study was performed to evaluate the presence of GBS in pregnant women and their newborns in Tabriz, Iran. Vaginal specimens were collected from 965 women who were candidate for vaginal delivery for bacteriological study of group B streptococci. Several samples from various sites of the newborns' body (ear canal, nose, navel, and groin) were also obtained to study the colonization rate in newborns after vaginal delivery. Identification of GBS strains was accomplished by bacteriological and serological tests. During the study period, 327 microorganisms were isolated from vaginal specimens of pregnant women from which 5.2% were Streptococcus agalactiae. Serotypes of S. agalactiae strains in our study were Ia (17.6%), Ib (13.4%), II (14.2%), III (9.5%), IV (8.2%), V (19.5%) and nontypable (17.6%). All of the newborns were followed up for eight weeks. Low carriage rate of GBS in vaginal canal of women in this area and probably lack of more virulent serotypes of GBS may explain the rarity of disease due to Streptococcus agalactiae in our region.