BACKGROUND: Increased dental caries and dental lesions have made preventive measures, especially among children, inevitable. This study investigated elementary schoolgirls’ mothers’ level of knowledge on preventive methods against dental caries. METHODS: In this cross-sectional study, mothers of 250 schoolgirls were randomly selected from five regions of Tehran, Iran. Their knowledge about fissure sealant therapy and fluoride therapy was evaluated using a questionnaire. Data was analyzed by analysis of variance and independent t-tests in SPSS. RESULTS: Mothers’ knowledge about fissure sealant therapy was lower than fluoride therapy. Very low, low, and moderate levels of knowledge were detected among nearly a quarter, 47.5%, and 22.6% of the participants, respectively. Only 5.4% of the subjects had acceptable level of knowledge on preventive dentistry methods. There were significant correlations between mothers' level of knowledge and their education level and occupational status. CONCLUSION: Educated mothers and working mothers had greater knowledge than did housewives. Dentists have a crucial role in increasing mothers' knowledge.