To obtain an aqueous coating agent which can form a coating film excellent in resistances to water, oil, and chemicals and in adhesion to many materials by incorporating a polyolefin elastomer and an acid-modified polyolefin and/or a higher fatty acid salt into the same and homogeneously dispersing solid components in an aqueous phase to give an aqueous dispersion.

This aqueous coating agent is prepared by melt mixing and kneading a basic substance and water into a melt mixture comprising a polyolefin elastomer and an acid-modified polyolefin and/or a higher fatty acid salt in such an amount of water that the total water concentration is 3-25 wt.% to thereby neutralize and/or saponify at least part of the acid-modified polyolefin and/or the higher fatty acid salt and to thereby disperse solid components in an aqueous phase. Preferably, this coating agent is an aqueous dispersion containing the acid-modified polyolefin and/or the higher fatty acid salt in an amount of 0.5-30 pts.wt. based on 100 pts.wt. polyolefin elastomer.