A self-dispersible coloring agent represented by formula (II) below is prepared by incorporating a hydrophilic group into a coloring agent through a reaction of a hydrophilic group-containing halide represented by formula (I) below and the coloring agent in the presence of a Lewis acid catalyst: X-L-R.sup.1 (I) (the coloring agent)-L-R.sup.1 (II)wherein L represents a single bond or --C(.dbd.O)--; R.sup.1 is selected from the group consisting of a substituted or unsubstituted C.sub.1-C.sub.20 alkyl group containing a hydrophilic group, a substituted or unsubstituted C.sub.6-C.sub.20 aryl group containing a hydrophilic group a substituted or unsubstituted C.sub.2-C.sub.20 heteroaryl group containing a hydrophilic group and a substituted or unsubstituted C.sub.7-C.sub.20 arylalkyl group containing a hydrophilic group; and X is one of: --F, --Br, --I and --Cl. may be obtained conveniently through a one-step process. The ink composition containing the self-dispersible coloring agent provides effective long-term storage stability and dispersion stability using a one-step process.