Objective Actinomyces are members of the indigenous oral microbiota which have been implicated in root caries, but their role in childhood caries initiation and progression is not well - understood. The distribution of Actinomyces in supragingival plaque on the primary teeth and the relationship between oral Actinomyces spp. and childhood caries primarily were investigated. Methods Forty children aged from three to five years old were divided into two groups. Twenty children were caries - free and twenty were caries - susceptible. Dental plaque samples from different places of the teeth were collected with sterile toothpick and polymerase chain reaction was performed with specific primers which were designed for this research. Results Actinomyces spp. were detected 100% in the cariesfree group, while 95% in the caries - susceptible group. There was no significant differences between the two groups （ P >0.05）. Actinomyces naeslundii, Actinomyces odontolyticus, Actinomyces gerencseriae, Actinomyces israelii and Actinomyces viscosus all could be detected in both groups. The prevalence of Actinomyces naeslundii, Actinomyces gerencseriae and Actinomyces odontolyticus were higher in caries- free group than those in caries- susceptible group （ P0.05）. Conclusion Actinomyces is the main colonized bacteria in the supragingival plaque of children. The prevalence of the Actinomyces spp. may have a negative relationship with the childhood caries, and has nothing to do with different places of the teeth.
