Provided are a navy blue water based ink composition for a ballpoint pen comprising a colorant, water and a dispersant, wherein at least cobalt phthalocyanine blue is used as the colorant, and a pH of the ink falls in a range of 7 to 10, and a ballpoint pen occulding the water based ink composition. Cobalt phthalocyanine blue has preferably a diameter of 500 nm or more and a content of 0.05 to 30% by weight based on the total amount of the ink composition.
