A gas-solid two-phases flow in a vertical pipe was investigated experimentally. Particle velocity and concentration were measured by an optical fiber probe, and gas velocity by a Pitot tube. Two kinds of polystyrene spherical particles were used, the mean diameters of which were 0.406 and 1.50 mm, and the pipe diameter was 40 mm. It was found that the concentration distribution has a maximum at the pipe center. The distribution of particle velocity is nearly flat for both particles. The distribution of gas velocity is strongly affected by the particles. In order to evaluate the degree of the particle influence on the distribution of gas velocity, a displacement thickness was considered and obtained for the present gas flow. The displacement thickness is found to correlate well with the mean concentration.