Statement of Problem: The mother’s mood and her attitude towards health services, dental treatment and their effects on her child’s oral health have already been studied. To the best of our knowledge, no research evaluating the direct effect of mothers’ depression on the child’s oral hygiene was found. Considering the fact that maintaining the child oral hygiene may depend on the mother’s willingness and attitude, the issue of maternal depression’s effect on the child’s oral heath is a subject for research.Purpose: The aim of this study was to evaluate the effect of mothers’ depression on their 5-12 year old children’s oral health.Materials and Method: For this descriptive and cross- sectional study, 358 mothers and their children aged from 5 to 12 years (mean=8.7±1.96) were selected through convenient sampling from the department of pediatric dentistry of Mashhad University of Medical Sciences. The children’s oral hygiene was determined, using OHI-S index. The mothers’ depression was assessed using 21 items Beck depression questionnaire. The collected data were analyzed, using SPSS Ver. 7.5. Descriptive and analytic outputs were obtained. Analysis of variance, t-student, and Chi-Square tests were performed to analyze the data.Results: There was a statistically significant difference between the means of Debri Index (DI) in the two groups of children with mothers with and without clinical depression (1.37±0.37 and 1.25±0.38 respectively) ( p <0.05). These results were confirmed by Chi-square test based on the frequency of children with good and poor debri Index.Conclusion: Based on the above results, oral hygiene in children of mothers with clinical depression is poorer than those with mothers without clinical depression. Children need emotional support, education, supervision and help of their mothers in order to perform their routine oral hygiene practice. Therefore, for improvement of the children’s oral health, their mothers’ mood is of great significance.Key words: Mother, Depression, Dental care for children