Background and Objectives: Caries in primary dentition affects the quality of child’s life and can interfere with the child's daily activities and growth process. This disease is affected by various factors such as diet, oral hygiene and socioeconomic factors. Considering the importance of the awarness of mother in a child’s life, the aim of this study was to investigate the relationship between the dmft index and the level of mothers’ awareness related to oral hygiene. Materials and Methods: This cross-sectional study was conducted on 432 mothers with children under 7 years old. After determining the dmft index, the children's demographic information and the mothers' awareness level were evaluated with 13 questions. In order to analyze the data, Kruskal-Wallis test and Pearson's correlation coefficient were used. Results: The mean score of awareness for mothers with boys and girls respectively was 3.70±2.25 and mothers 3.58±2.36 with no significant difference (P=0.757). The most correct answers from mothers to questionnaire’s questions, were given to the size of toothpaste for children aged 3 to 6 years old (70.8%) and the time to start flossing for children (38.2%). The relationship between mother's awareness and dmft index was not significant (P=0.076). Conclusion: Mothers' knowledge level had no significant relationship with children's dental caries, but mothers' knowledge of caries prevention was lower than mean. Although maternal knowledge is only one of the several factors that can influence children's oral health behaviors, mothers' education should be considered as an important intervention to caries prevention.