The effects of liquid property on air entrainment and oxygen transfer characteristics of a plunging jet reactor are investigated in air-corn syrup solution system with changing the viscosity up to 40.5 mPa s. The effect of liquid property on air entrainment rate is divided into three regions. The transition points of the regions are represented with jet Reynolds number. The change in air entrainment rate with liquid property is discussed in relation to the change in jet surface disturbances. Empirical correlations are also presented to predict the air entrainment rate, gas holdup and oxygen transfer coefficient. The oxygen transfer performance of the reactor is superior to that of the conventional bubble columns and stirred tank reactors over the range of viscosity from about 1 to 40.5 mPa s. It is concluded that the plunging jet reactor is one of the most promising bioreactor treating a viscous fermentation broth.