Provided is a water-based ink composition for a ballpoint pen characterized by comprising at least colored resin particles which have an average particle diameter of 2 to 20 μm and which are non-thermoplastic in a proportion of 5 to 30% by weight based on the total amount of the ink composition and non-colored particles having a glass transition point of lower than 0° C. The average particle diameter of the non-colored particles described above is controlled preferably to 0.01 to 10 μm. The water-based ink composition for a ballpoint pen described above further comprises preferably at least one selected from ethylene oxide or propylene oxide adducts of glycerin and ethylene oxide or propylene oxide adducts of diglycerin in a proportion of 1 to 30% by weight based on the total amount of the ink composition. The above water-based ink composition for a ballpoint pen is stable with the passage of time and excellent in a writing performance, erasability by an eraser and abrasion resistance.