To obtain a pigment derivative and resin by dissolving an organic pigment and modifying it under a mild condition without using concentrated sulfuric acid, fuming sulfuric acid, etc., useful for improving dispersibility, dispersion stability, noncohesiveness, etc.

(A) An organic pigment (e.g. quinacridone-based one, indanthrone-base one, isoindolinone-based one, etc.) is dissolved in (C) an aprotic polar solvent (e.g. dimethyl sulfoxide, tetramethylurea, sulforlane, etc.) and is reacted with (D) a modifying agent [e.g. an amino group-containing (meth) acrylic acid ester, an amino group-containing (meth)acrylamide, etc.] preferably at -30°C to 120°C. Preferably the amount of the component B added is 0.1-10 equivalent base on 1 equivalent of the component A, that of the component D is 1-30 equivalent based on 1 equivalent of the component B and the amount of the component C added is 5-200 pts.wt. based on 1 pt.wt. of the component A.