The injection nozzle with control plate was developed in order to stabilize the upward submerged gas jet. The gas hold-up of bath and the volumetric mass transfer coefficient for gas-liquid reaction were enhanced when the control plate was placed near the nozzle, because the injected jet was dispersed into small bubbles at the plate. The knocking frequency of jet decreased as the plate was approached toward the nozzle and became to zero at the critical distance from the nozzle ( L_crit). L_crit. increased with increasing stagnant pressure of jet and slightly decreased with increasing nozzle Mach number. A good relationship was obtained between jet core length and L_crit. The effect of control plate on the jet stability was observed in mercury bath as well as in water bath.