Overall the diets of Australian schoolchildren are suboptimal, but differences in nutrient and food intake on school versus non-school days have not been assessed. The aim of this study was to examine differences in nutrient and core and non-core food intake on school days versus non-school days in Australian schoolchildren aged 6-16 years. Cross-sectional analysis of the 2007 Australian Children's Nutrition and Physical Activity Survey. Dietary intake was assessed via one 24-h dietary recall. A school day was defined as Monday-Friday, a non-school day included Saturday, Sunday and public/school holidays. Independent t-tests and χ(2) tests were used to assess differences in continuous and categorical variables, respectively. Multiple linear and logistic regression was used to adjust for confounders. Forty-eight per cent of recalls were completed on a non-school day. On non-school days primary schoolchildren aged 6-11 years (n = 1334) and secondary schoolchildren aged 12-16 years (n = 1362) had significantly higher absolute intakes of sugars, total fat and saturated fat (all P < 0.05). In addition the energy density of foods consumed was greater (P < 0.001), but there was no difference in the energy density of fluids. The sodium density of the diet did not differ across day types. On non-school days, total core food intake was ~30% higher and children were more likely to consume sugar-sweetened beverages, fried potatoes and take-away pizzas and burgers (all P < 0.05). Important differences in the intake of sugar, total fat, and saturated fat and noncore foods exist on non-school days compared to school days in Australian schoolchildren. To improve the diets of schoolchildren there is scope for strategies that target non-school day eating practices.