In this study, characteristics of adiabatic two-phase flow through horizontal pipe having smooth expansion are investigated numerically and experimentally. Effects of volumetric void fraction and internal diameter of the pipe on hydrodynamic characteristics of the two-phase flow are examined using average diameter of the bubbles injected. Air and water are chosen as the fluid couple. Flow rate for water is kept constant at 3 lt/s while those for air are taken as 50 and 61 lt/min. Thus, volumetric void fraction of 21.74 and 25.31 % are obtained for the two-phase flow considered, respectively. Eulerian-Eulerian Model and Reynolds Stress Model (RSM) are employed for modeling of two-phase flow and turbulence. Numerical results are then compared to the experimental data that was previously obtained by dual optical probe that measures local parameters of the two-phase flow (Deniz, 2009). The comparison shows that using the assumption of the average bubble diameter for numerical modeling gives reasonable results for developed and stratified flow.