Provided is an ink composition that is for a water-based ballpoint pen, that is capable of generating a drawing line with a deep shade of black as obtained from a calligraphy ink stick liquid, and that produces distinctive aroma.　An ink composition for a water-based ballpoint pen according to the present disclosure is characterized by at least containing borneol and a black pigment that satisfies requirements X to Z.　X: The 50% particle diameter (D50) in a cumulative particle size distribution on a volumetric basis is 0.2-1.0 μm. Y: The 10% particle diameter (D10) in a cumulative particle size distribution on a volumetric basis is 0.1-0.3 μm. Z: The 90% particle diameter (D90) in a cumulative particle size distribution on a volumetric basis is 1.0-5.0 μm.