A water-based ink composition for a ballpoint pen containing 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 60° C. or higher. The average particle diameter of the non-colored particles is preferably to 0.01 to 10 μm. The ink composition preferably includes 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.