The effect of oil dispersion on the flow characteristics in bubble column is experimentally examined. The kind and concentration of oil are changed, and oil is dispersed in tap water. The flow pattern of bubbles and the oil dispersion are observed, and the distribution of oil droplet, the gas holdup and the volumetric coefficient are measured. The flow characteristics in bubble column are changed due to small oil droplets. The gas holdup becomes higher, but the volumetric coefficient becomes lower than those in tap water. From these, it is concluded that the mass transfer coefficient becomes lower in the oil dispersion system.