The present invention provides a water-based ink composition for a ballpoint pen that is less likely to cause bleeding of a written trace in writing, provides a favorable written trace without causing no blurring or line splitting, and excels in the storage stability of the ink composition; and a water-based ballpoint pen using the ink composition.
A water-based ink composition for a ballpoint pen comprising water, a coloring agent, a copolymer having a specific structure; and a water-based ballpoint pen using the ink composition.