To provide an oil-based ink composition for a ballpoint pen that hardly causes dripping and provides a smooth writing feeling.

The oil-based ink composition for a ballpoint pen includes: a colorant; and 0.1-3 wt.% of a stringy resin having a carbonyl group, specifically polyvinylpyrrolidone, a vinylpyrrolidone-vinyl acetate copolymer, a polymethacrylic acid ester, a polyacrylic acid-polymethacrylic acid copolymer, polyvinyl butyral, etc., based on the total ink composition, and includes at least 5-60% of propylene carbonate as a solvent.