The adsorption of ethane and propane in $K^{+}$ ion exchanged zeolite L has been studied using grand canonical ensemble Monte Carlo simulation. $CH_3$ and $CH_2$ groups of sorbate molecule were considered as pseudoatoms in calculation of potential, and the bond lengths and bond angles within a molecule were fixed during simulation. Average number of molecules per unit cell, number density of molecules in zeolite, distribution of molecules per unit cell, average potential per sorbate molecule, and isosteric heats of adsorption were calculated, and these results were compared with experimental results. For ethane the simulation results agreed considerably well with experimental ones over a wide range of temperature. The average potential of sorbate molecule decreased slowly with the increase of amounts sorbed in zeolite.