OBJECTIVE To find out different transmission ways of oral mutans Streptococci (MS) in nursery children. METHODS The study group included 44 nursery children between 3 and 4 years of age and 20 mothers. Dental plaque samples were collected with sterile toothpick and cultured on MSB plates for 48 h. Individual MS colonies representative of the colonial morphologies were subcultured on TPY plates. These strains were biochemically identified to species level. AP-PCR fingerprinting analysis was preformed after identification. RESULTS MS was isolated in oral cavities of 65.9% children in 44 babies and 50% pairs in 20 mother-child pairs. A total of 98 MS isolates from 44 children and 20 mothers were isolated. Thirty-two different amplitype were identified in 10 mother-child pairs colonized by MS and there were similar genotypes in 7 pairs of mother-child. Twenty-nine different amplitype were identified in 24 nursery children, and there were 2 genotypes of MS isolated repeatedly among 13 nursery children. CONCLUSIONS The presence of matching genotypes of MS among nursery children and their mothers suggests horizontal and vertical transmission.