To reduce the uncertainty in predicting pressure drop for two-phase flow through spherical particle beds, especially composed of small-sized particles that adversely affect the cooling, an experimental study was performed. A series of experiments were performed to measure the pressure drop of upward two-phase flow through well-packed spherical particle beds with 2, 3.5, and 5 mm diameter particles under isothermal conditions varying the gas flow rates with no water inflow at the bottom. Based on the experimental results and the results of our previous study related to the modification of Ergun constants, a new improved model for prediction of the two-phase flow pressure drop through porous media was proposed. The adequacy of the proposed model was verified by comparison with various existing experimental data for particle diameters of 3.18-6.35 mm and the superficial air velocity of 0-0.8 m/s. (C) 2018 Elsevier Ltd. All rights reserved.