To obtain a water-based coating composition which has excellent pigment dispersion, has satisfactory adhesion especially to plastic substrates, and gives a film excellent in drying properties, water resistance, heat resistance, and alcohol resistance.

This composition comprises a combination of a water-compatible acrylic resin with a carboxyalkylcellulose nitrate in which the number of nitrate substituents and that of carboxyalkyl ether substituents are 0.2 or larger and 0.05 or larger, respectively, per anhydrous glucose unit.