Polyurethane (PU) emulsions were prepared from polytetramethylene adipate diol, toluene diisocyanate, dimethanol propionic acid, and so forth. The effects of calcium ion on the stability of PU emulsion as well as on the water-resistance property, tensile strength, and tensile yield of PU film were discussed. The results show that calcium ion can quickly damage the stability of PU emulsion. Meanwhile, calcium ion can distinctly counteract the unfavorable effects water has on the tensile properties of PU film. (C) 2003 Wiley Periodicals, Inc.