This Study provides experimental data oil the performance of microchannel contactors for CO2 absorption. An aqueous solution of piperazine (PZ) activated N-methyldiethanolamine (MDEA) and a mixture Of CO2/N, were selected as the working fluids. Three different sizes of microchannels, with hydraulic diameters of 0.5, 1, and 2 mm and the same length of 180 mm, served as the contactors. With a decrease in the hydraulic diameter the larger surface to volume ratio can be achieved. The mass transfer rates increased considerably, and the size effect of mass transfer was observed. Various operating parameters, including the activator, the temperature of gas and liquid flow, the inlet CO2 molar fraction, the superficial gas and liquid velocities, and the operating pressure were also evaluated. The results obtained illustrated a great potential of microchannel contactors when they were applied to the separation of CO2.