To provide a water-based ink composition for ball point pens that shows excellent lubricant properties, the reduced ball sink, even when the pen is filled with the ink and used for writing, and gives the smooth pen touching and retains the writing performance.

The objective water-based ink composition for ball point pens comprises coloring agents, water and a specific mercaptobenzothiazole derivative represented by general formula (1) (n is an integer of 1-3; X is H, an alkali metal or an amine) as a lubricant in an amount of 0.01-10 wt.%.