BACKGROUND: Inhalation of fine particulate matter (PM) can cause systematic inflammation and oxidative stress, which may further aggravate the development and progression of asthma. Although nutritional intake of fatty acids and antioxidants may attenuate some effects of fine PM, the role of the inflammatory potential of diet has not been addressed. Therefore, we aimed to investigate possible modulatory effects of dietary inflammatory potential on the association of indoor air pollution and childhood asthma-related outcomes. METHODS: In a sample of 501 children (48.1% males, aged 7 to 12 years) from 20 public schools located in Porto, Portugal, we evaluated airway reversibility, exhaled nitric oxide levels, atopy and current respiratory symptoms. Dietary inflammatory index was calculated based on information collected through a reported 24-hour recall questionnaire, and participants were categorized as having an anti-inflammatory or pro-inflammatory diet. Concentrations of indoor PM2.5 and PM10 were measured to assess indoor air quality. Generalized linear mixed models were used to investigate the proportion of effects explained by the exposures to PM2.5 and PM10. RESULTS: After adjustment, the exposure effect of PM2.5 and PM10 levels on children with asthma was higher for those having a pro-inflammatory diet (OR= 1.44, 95% CI: 1.01 to 2.21 and OR=1.29, 95% CI: 1.03 to 1.68, respectively) compared to those having an anti-inflammatory diet. CONCLUSION: These findings suggest that the quality of diet might affect the association of indoor pollution and asthma in children, highlighting the relevance of children's diet as a potential protective factor to pollutants exposure in childhood asthma.