An investigation was conducted to compare the syringe gas test system with the reading pressure technique (RPT). A series of mixtures of neutral detergent fibre (NDF) and maize starch were incubated using both systems and the ratios (wt/wt) of maize starch in the mixtures were 0, 10.0, 20.0, 25.0, 33.3, 50.0, 55.6, 62.5, 71.4, 83.3 and 100%. The gas production (GP) was recorded at 0, 2, 4, 6, 9, 12, 24, 36, 48 and 72 h. There was no significant difference in potential GP between two systems (corrected to 200 mg substrate basis) (P>0.05), while the GP at a short time of incubation were lower in the RPT system than in the syringe and the rate constant of GP was significantly higher in the syringe (P<0.05). However, a strong relationship was observed between the 24 h GP values (GP_24h) in the syringe system and the RPT, which was described by: GP_24h for the syringe system (ml) = 1.2628 × GP_24h for the RTP system (ml) + 6.2592 (R²=0.9784; P<0.01; n = 132). It is indicated that the GP_24h in the two systems can be revised reciprocally and appropriate system could be chosen according to the research objectives and characteristics of both methods.