Background/purpose Previous studies have suggested that mouth breathing has harmful effects on oral health in children, but the evidence has been insufficient. To investigate the association of mouth breathing with oral health in school children aged 8–11 years from Nagpur city , India Materials and methods Cross-sectional data were obtained from March to April 2019. A questionnaire was used to investigate children's mouth breathing habits and personal/family histories related to allergic disease. Oral health status was determined through a clinical oral examination. Data were analyzed with multivariable logistic regression. Results In total, 1007 children were included. We observed no association between mouth breathing and dental caries in children. However mouth breathing was associated with child's tonsillitis and was identified as a possible risk factor for class II dental malocclusion. Conclusion We confirmed the positive association between mouth breathing (especially during sleep) and dental class II malocclusion. However the influence of mouth breathing on dental caries remains uncertain. An intervention trial is required to evaluate whether the prevention of mouth breathing can reduce the risk of dental problems.