In this research two-phase slug flow regime in a T-junction branching divider is examined in two regular and irregular groups. Simulation is accomplished by OpenFOAM™ open source software. Simulation uses single fluid with volume of fluid (VOF) method to follow gas-liquid two-phase flow interface. Constant velocity boundary condition for inlet, constant pressure for outlet boundaries and no slip boundary condition are considered for fixed walls. Since slug flow regimes are one of the most complex two-phase flow regimes which its behavior could result in serious damages to the downward equipment's; the present research concentrates on the examination of slug flow behavior in the downstream of the T-junction. This study has concluded that using T junction eliminates flow fluctuation so the pressure and air velocity values decrease. Although the inlet of the vertical branch with cross section of 5×5 cm2 is not fully effective in decreasing upward slugs, but with increasing size of the inlet vertical side-branch from 5×5 cm2 to 10×5 cm2 and 20×5 cm2, pressure value of two-phase flow in the whole duct decreases. The consequences are the slug flow decreases in downstream but the plug flow grows up which means the objectives of the research has been accomplished. To verify the numerical results, comparison was made with the well justified previous works. The agreement was encouraging.