The gas slippage phenomenon is usually observed when gas flow through porous media under low pressure. and has received an increasing attention for its importance in science and engineering. In the past decades, although many theoretical, numerical and experimental works have been done to predict the permeability of a square array of circular cylinders, little literature is available in studying the slippage effect on permeability. In this paper, the gas slippage effect on the permeability of circular cylinders in a square array is studied theoretically. The permeabilities at low and high solid fractions are derived with cell model and lubrication theory by coupling with a first-order slip boundary condition. The present results are finally validated through a comparison with some available results. (C) 2011 Elsevier Ltd. All rights reserved.