Abstract: The effects of superficial gas velocity, catalyst loading, liquid properties and internal fitting on gas holdup of air/water, air/paraffin oil and air/catalyst/paraffin oil were investigated in a 0 2 m diameter, 4 2 m height slurry bubble column reactor operating with methanol synthesis copper-based catalyst and methanol dehydration catalyst. The experimental data showed that gas holdup increased with superficial gas velocity no matter whether there was a heat exchanger. However, no matter whether there was a heat exchanger, gas holdup decreased with the increase of catalyst loading. The existence of heat exchanger favored the increase of gas holdup. The gas holdup in the air-water system was slightly higher than in the air-paraffin system. Empirical correlations for gas holdup data were proposed.