Gas flow in porous media occurs in various engineering devices such as catalytic converters and fuel cells. In order to improve the performance of such devices, it is important to understand transport phenomena in porous media. In porous media with pores as small as a molecular mean free path, molecular motions need to be directly considered instead of treating gas flow as a continuum, and effects of complicated channels need to be taken into account. Therefore, such gas flow was analyzed by using the direct simulation Monte Carlo (DSMC) method, which is the stochastic solution of the Boltzmann equation. Numerical simulations of gas flow driven by pressure gradient without surface reaction were performed to clarify transport phenomena in porous media imitated by arranging nanoscale solid particles randomly. The effects of pressure gradient, diameter of particles and porosity on gas flow rates and permeability of porous media were investigated.