A filament for cosmetic brush is constituted by a polyester resin filament having many projections over its entire surface, wherein the polyester resin is polytrimethylene terephthalate and/or polybutylene terephthalate, the polyester resin contains glass particles of 1 to 2 μm in average particle size by 0.3 to 1.0 percent by weight as the inorganic particles, the thermal conductivity of the glass particle is in a range of 5 to 7 times that of the resin, and the projections are formed over the entire surface of the cosmetic filament by the glass particles covered with the resin.