Grand Canonical Monte Carlo (GCMC) simulations were employed to study the adsorption behaviors of CH4 and H-2 onto silicalite-1 and a recently developed type of "polymers of intrinsic microporosity" (PIMs), PIM-1 polymer. COMPASS and PCFF force fields were introduced to calculate adsorption isotherms at 77 and 298 K, respectively. The COMPASS and PCFF force fields have been applied to simulate the behaviors of small-molecule gases and it was found that PCFF was more reliable for H-2. The adsorption of CH4 onto PIM-1 was found, for the first time, to be 60-68% higher than onto silicalite-1 at 77 K but lower than that at 298 K. The amorphous pores in PIM-1 were responsible for the disappearance of adsorption sites with increasing temperature; this occurred to a greater extent than in the ordered microporous structure of silicalite-1. Some approaches should be adopted to improve the micropores concentration of PIM-1. The simulation results of H-2 adsorption onto PIM-1 and silicalite-1 by PCFF force field agreed well with the experimental data. It revealed that adsorption onto PIM-1 was not stable with only a heat of absorption 1.57 kcal/mol. If the structure of PIM-1 is optimized to allow a heat of absorption at a level of 3-5 kcal/mol, its hydrogen storage ability could be substantially improved. (C) 2011 Elsevier Ltd. All rights reserved.