PURPOSE: To obtain the subject compsn. which has such an excellent lubricity as to reducing the abrasion of a ball holder, and is excellent in durability and feeling during writing.

CONSTITUTION: The objective water-base ink compsn. contains a water-sol. dye or a water-dispersible pigment, a water-sol. org. solvent, water, and at least one compd. selected from the group consisting of a thiodicarboxylic acid and its alkali salt, amine salt, and alkanolamine salt and represented by the general formula: S(RCOOX)2 (wherein R means a single bond, 1-6C alkylene, alkenylene, or phenylene; and X means H, an alkali salt, amine salt, or alkanolamine salt).