The paper reported two-phase flow pressure drop results of R22 during condensation in a horizontal stainless steel rectangular microchannel with the hydraulic diameter of 0.952 mm. Tests were conducted with saturation temperatures of 40-50oC

mass fluxes of 200-800 kg/m2 s and vapor qualities from 0 to 1. The results show that pressure drops in the test section account for more than 95% of the measured pressure drops while the fractions of the expansion pressure drops at the outlet of the test section are small enough to neglect. Pressure gradients of R22 increase with mass flux and vapor quality especially in high vapor quality regions while decrease with the saturation temperature. Pressure gradients of R152a are lower than the data of R22 when compared with the same experimental conditions.