To obtain a colorant composition for unsaturated polyester resins, which is free of gelation, thickening, sedimentation, segregation, or the like and has a high shelf stability, and to obtain an unsaturated polyester resin composition and its preparation.

A fine powder form colorant composition for unsaturated polyester resins comprises a pigment and/or oil-soluble dye and a resin, wherein at least one resin selected from a polystyrene, a low-molecular weight polystyrene, a low-molecular weight acrylic styrene and a low-molecular weight acrylic resin is contained as the resin.