ABSTRACT Objective To evaluate the internal validity and reliability of an index developed to assess the nutritional quality of meals. Methods The Main Meal Quality Index is composed of ten components. The final scores range from 0-100 points. The index performance was measured using strategies for assessing content validity, construct validity, discriminant validity and reliability. The analyses were performed using the Stata statistical software at a 5% significance level. Results The index was positively associated with carbohydrates, vegetable proteins, fibers, vitamins, folate and potassium and negatively associated with energy, total fat, saturated fat, animal protein, cholesterol, phosphorus, sodium, added sugar, and cholesterol biomarker. Significant differences were found between the two groups with marked disparities in dietary quality, smokers (50.2 points) and non-smokers (53.5 points). Conclusion The index might be a useful tool for assessing the nutritional quality of meals and for monitoring and comparing groups.