Abstract: Polyurethane (PU) foams were successfully prepared from liquefied corn stover polyol by varying the amount of blowing agent---water. The effects of water amount on the mechanical and thermal properties of PU foams were investigated by means of universal tensile machine, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results showed that with an increase of water amount, tensile strength and elongation rate at break of the PU foams first increased and then decreased, their maximum values reached 1.87 MPa and 189.7% respectively. Furthermore, with an increase of water amount, the initial decomposition temperature decreased, glass transition temperature increased and the range of glass transition temperature expanded. The properties of PU foams can be changed by varying the amount of water.