Air-water co-current (horizontal) flow experiments were carried out to measure pressure drop and liquid holdup in a 1 mm (ID) diameter glass tube packed with 55 mu m nearly monodisperse glass spheres. The measurements allowed calibration of a two-dimensional hydrodynamic model based on the volume-averaged mass and momentum balance equations to describe the cocurrent two-phase flow in packed bed microreactors. The heterogeneous nature of the packed bed was taken into account via incorporation of radial non-uniformities of the bed. The liquid and gas velocity fields are characterized by a significant non-uniformity with major variation occurring in the region extending up to a distance of two particle diameters from the wall bounding surface and with a maximum located in the high porosity zone. The model shows considerable sensitivity of two-phase flow with respect to capillary pressure, which has the tendency to spread radially the liquid flow to approach radial uniformity. The capillary pressure causes liquid phase displacement from the high-porosity to the low-porosity region resulting in smaller/higher fraction of the liquid/gas flowing through the microreactor cross-section leading to channeling and thus to an increase/decrease of liquid/gas flow through the core area. In packed bed microreactors, two-phase pressure drop is very large and is considerably influenced by the capillary forces, especially at higher reactor-to-particle diameter ratios. (C) 2012 Elsevier Ltd. All rights reserved.