Gas holdup in a pressurized bubble column with diameter of 45 mm was studied experimentally for carbon dioxide-water and nitrogen-water system. The diameter of single nozzle used as gas disperser was 1.0 or 4.0 mm. Pressure effect on gas hold-Lip was not observed when a single nozzle of 4.0 mm was used, but when a single nozzle of 1.0 min was used, the pressure effect was observed. Gas holdup for the system of nitrogen-water increased with the pressure. On the other hand, gas holdup for the system of carbon dioxide-water showed the maximum at the pressure of 0.6 MPa. To explain these phenomena by bubble behavior, bubble size were observed by the laser-Doppler device and the critical gas velocity for the transition from the single bubble formation mode to the bubble fort-nation out of gas jet was observed by visual observation in the pressurized cell.