Harvesting time is one of the main factors that influences grain quality, largely due to their exposure to biotic and abiotic factors during pre-harvest. As such, this study aimed to assess corn grain quality in response to different harvesting times in the municipality of Campo Novo do Parecis, Mato Grosso state, Brazil. A randomized block design was used with a strip-plot scheme, consisting of three corn hybrids (NS90 PRO, NS92 PRO 2 and BG7439), five harvesting times (0, 7, 14, 21 and 28 days after physiological maturity - DAPM), with three repetitions. The variables grain yield, 1000 grain weight, bulk density, electrical conductivity and proximate composition were analyzed at each of the proposed harvesting times and lipid composition was assessed only at 0 and 28 DAPM. Data were submitted to ANOVA, regression analysis and Tukey’s test (p ≤ 0.05). Delayed harvesting influenced all the variables studied, except ash concentration. The longer the grains remain on the plant after physiological maturity, the worse the grain yield and their physical, chemical and nutritional quality.