In this work an experimental study of local void fraction distribution in square arrangement rod bundle channel 3 * 3 under bubble flow regime was carried out. Measurements were performed with conductivity probe help, which was introduced into the flow through an angular or side rod at an angle of 15° to the flow. This method made it possible to determine the local void fraction close to the walls of the rods and in the narrow gap between them. Measurements have shown that a dome-shaped profile of local void fraction is realized in the gap between the side rode and the central one, while a saddle-shaped distribution of the void fraction is observed on the line connecting the central and angular rods. Also the effect of the spacer grid on the distribution of the gas phase in the channel was shown.