OBJECTIVE:To develop a diet quality index and to analyze socioeconomic factors associated with low child diet quality. METHODS:A cross-sectional study was performed with a representative sample of 1,282 children aged between seven and ten years, living in the city of Vitória, Southeastern Brazil, in 2007. Children were randomly selected from 26 public schools and six private schools. Data on socioeconomic characteristics and life habits of children were obtained from a structured questionnaire, sent to homes and preferably completed by mothers. A food frequency questionnaire was created from studies performed with Brazilian children and tested in a public school. An index entitled Índice de Alimentação do Escolar (ALES -School Child Diet Index) was designed to assess diet quality, taking in consideration the nutritional recommendations for the Brazilian population and the habit of having breakfast. The association between diet quality and socioeconomic factors was analyzed using multinomial logistic regression. Adjusted odds ratios and 95% confi dence intervals were estimated for the variables that remained in the model. RESULTS:According to the ALES index, approximately 41% of the children studied had low diet quality (boys= 37.7%, girls= 42.7%, p= 0.179). There were no signifi cant differences between sex, age, maternal employment status and living with the mother and diet quality. The variables that remained associated with low diet quality were low maternal level of education (OR= 3.93; 95% CI: 2.58;5.99), father not present in the household (OR= 2.03; 95% CI: 1.68;2.99) and not having lunch at the table (OR= 1.47; 95% CI: 1.12;1.93). CONCLUSIONS:Low maternal level of education increased the probability of a child not consuming a good quality diet, whether due to lack of access to healthy foods and adequate information or poorer ability to discern what is healthy.