Glycerol has become readily available from biodiesel industry. High functionality and relatively low price make it a potential building block to produce value-added derivatives such as acrolein. In this study, low-pressure packed-bed gas-phase dehydration of glycerol was investigated in presence of various solid acid catalysts, including H3PO4/activated carbon catalyst. Dehydration mechanism over H3PO4/activated carbon catalyst was validated. In the presence of H3PO4/activated carbon catalyst, yield of acroelin (66.8%) and selectivity to acrolein (84.0%) were achieved at the temperature of 260 degrees C and the pressure of 0.85 bar.