PURPOSE: To obtain the subject composition capable of giving plastic molded products developing no color deepness unevenness or difference and discoloration with time, by dispersing a colorant in a thermoplastic resin having specific physical properties.

CONSTITUTION: This colorant composition is obtained by dispersing 30-60wt.% of a colorant such as carbon black in a thermoplastic polymer, pref. a noncrystalline polyester polymer or styrene-based polymer, having a glass transition temperature of 40-80°C determined by differential thermal analysis and a number-average molecular weight of pref. ≤50000 with the weight-average molecular weight at least five times the number-average molecular weight. This composition can be used in the form of sphere or amorphous powder 3μm in volume-average particle size or amorphous granules, beads or pellets 20μm in size.