The pressure drop of gas-liquid two-phase flow in microchannel is of fundamental importance in heat and mass transfer processes. In this work, the pressure drop of gas-liquid two-phase flow in horizontal rectangular cross-section microchannels was measured by a pressure differential transducer system. Water, ethanol and n-propanol were used as liquid phase to study the effects of capillary number on pressure drop; air was used as the gas phase. Four microchannels with various dimensions of 100 mu m x 200 mu m, 100 mu m x 400 mu m, 100 mu m x 800 mu m and 100 mu m x 2000 mu m (depth x width) were used for determining the influence of configuration on the pressure drop. Experimental results showed that in micro-scale, the capillary number also affected the pressure drop remarkably, and in spite of only one-fold difference in aspect ratio, the variation of pressure drop reached up to near three times under the same experimental conditions. Taking the effects of aspect ratio and surface tension into account, a modified correlation for Chisholm parameter C in the Chisholm model was proposed for predicting the frictional multiplier phi(2)(l), and the predicted values by the proposed correlation showed a satisfactory agreement with experimental data.