Particles suspended in tube flows are known to migrate laterally due to the presence of inertial lift force and eventually focus on specific locations in the downstream cross section. In the flow of viscoelastic fluids, suspended particles also experience viscoelasticity-induced lift force. In the present paper, inertial migration of spherical particles suspended in square tube flows of Newtonian fluids or viscoelastic fluids are reviewed. The focusing positions of suspended particles appear at the center of channel faces, on the diagonals, at intermediate positions, at the center or near the corners of the square cross section, depending on the blockage ratio, the Reynolds number and the Weissenberg number. The particle focusing patterns experimentally obtained are discussed in relation to the lift force map in the tube cross section.