To provide an oily ink for ballpoint pens, that hardly cause the blurring of handwriting at the beginning of the writing, even when left in a state contacted with outside air for a long time.

This oily ink for ballpoint pens comprises a colorant, an organic solvent, and a copolymer comprising the constituting units of a monomer having at least carboxyl group in the molecule and the constituting units of a monomer having a styrene group, or a hydroxyl group-having polyvinyl butyral resin, and a silicone whose both ends are modified with amino groups.