A defoaming agent which can effectively eliminate foams generated in the occasions of preparation, coating, drying and baking of water-based paint, by addition thereof by itself, without combined use of other kind(s) of defoaming agent(s), and furthermore without impairing appearance of baked coated film of the paint or recoatability of the paint is provided. Such a defoaming agent for water-based paint has the composition comprising (1) polyoxyethylene hydrogenated castor oil triisostearates and (2) polyalkyl vinyl ether, polybutadiene, polybutene or polyisoprene, which are dissolved in (3) liquid normal paraffin, liquid isoparaffin or liquid cycloparaffin, at such a ratio that the blended amount of (1) occupies 2-90% by weight of the total composition.