An experimental and theoretical study of low Reynolds number compressible gas flow in a microchannel is presented. Nitrogen gas was used. The channel was microfabricated on an oxidized silicon wafer and was 50 mum deep, 200 mum wide and 24,000 mum long. The Knudsen number ranged from 0.001 to 0.02. Pressure drop at inlet and exit of the channel were measured and friction factor constant ratios were calculated at different mass flow rates in terms of Re. The results were found in good agreement with those predicted by analytical solutions in which a 2-D continuous flow model with first slip boundary conditions are employed and solved by a perturbation method with a proposed new complete momentum accommodation coefficient sigma. Consequently, using slip boundary conditions, one can well predict the mass flow rate as well as inlet/exit pressure drop and friction factor constant ratio for a three-dimensional physical system. (C) 2004 Elsevier Ltd. All rights reserved.