Water-based architectural paints commonly contain either mineral oil-based or silicone-based antifoams. Mineral oil-based antifoams generally reduce the gloss of paint films; thus, silicone-based antifoams are mainly used in the field of architectural paints. The relationship between the antifoaming performance and the particle size of hydrophobic silica for mineral oil-based antifoams was investigated and a novel mineral oil-based antifoam that provided a glossy surface to the paint films equivalent to the surface obtained with silicone-based antifoams and with excellent antifoaming performance compared to silicone-based antifoams was developed. The novel mineral oil-based antifoam exhibits better performance than silicon-based antifoam, and thus the former is a perfect alternative to the latter for use in architectural paints.