The objectives of this study were to study the fermentation kinetics of different carbohydrate fractions of maize grains of Chinese varieties based on in vitro gas production curve subtraction technique. Ten maize grain samples were extracted with either 80% ethanol or neutral detergent to obtain ethanol-insoluble residue (EIR) and isolated neutral detergent fibre (NDF). Then unfractionated maize grain (UCG), EIR and NDF were fermented in vitro and the gas production was recorded. Because fermentation characteristics of fraction A (sugars and organic acids) and B1 (starch and soluble fibre) were not directly measured, a curve subtraction technique was used to evaluate the gas production and fermentation of these soluble fractions. The results showed: 1. the proportion of different carbohydrate fractions averaged 10.3±1.1, 78.3±1.2, 11.8±0.6% and 0.6±0.2% on DM base for A, B1, B2 (digestible fibre) and C (indigestible residue) fractions, respectively; 2. there were high correlation coefficients among gas production of UCG, the A, B1 and B2 fractions; 3. there was no significant difference between observed kinetics parameters and those predicted by the Gompertz function for the A and/or B1 fractions; and 4. the A fraction had the significantly highest acetate to propionate ratio among fractions studied while the B2 fraction the lowest. In conclusion, the in vitro gas production curve subtraction technique was approved as a feasible approach to estimate fermentation kinetics of carbohydrate fractions of maize grains.