An ink composition for such a pressurized ball-point pen as is excellent in writing characteristics and is free from ink leakage to thereby be suitable for handwriting; and a pressurized ball-point pen. This ink composition for pressurized ball-point pen is one at least comprising a colorant, a solvent and silica wherein aggregates at least containing silica are contained and which ink composition exhibits a viscosity of 10,000 to 40,000 mPa.sec at 25ºC. The pressurized ball-point pen may be one comprising a closed contained and, accommodated therein, an ink filling tube filled with the above ink composition for pressurized ball-point pen together with a refill having a pressure gas sealed therein.