The results of the experimental study of downward bubbly flow in a vertical pipe of 20 mm i.d. are given. Water-glycerin solution was used as the test liquid. The experiments were carried out over the Reynolds number range from 1000 to 1500. The local flow parameters (local void fraction, liquid velocity, velocity fluctuations) were measured using the electrodiffusional technique. The experiments demonstrated the strong effect of the gas phase on the flow structure. The effect is manifested in increase in the wall shear stress and flattening the liquid velocity profile in the central part of the pipe. A significant deviation from the single phase flow takes place even at low gas flow rate ratios.