By performing Monte Carlo simulation, a reliability of mercury porosimetry, which is widely used for determining the distribution of pore sizes of porous media is investigated. The hypothetical porous media in which the exact distribution of pore sizes for differently given the pore lattice structures are known is constructed on the computer and subsequently the mercury penetration-retraction simulatiion studies are carried out. The tested types of porous media have 2-D square or hexagonal-triangular lettice structures, respectively, and they have the pore structure as the sphercal pores are located in each lattice sites and these pores are bonded by the cylindrical capillary pores according to the given lattice type. Also, the tested media have one of the distributions of pore sizes such as the normal, bimodal and skewed types. As the results, we found that the average pore sizes for such media can be measured accurately by the method of mercury porosimetry. However, the fraction of average distrubutions of pores measured by the method of mercury porosimetry. However, the fracton of average distrubutions of pores measured by the method tends to show higher values than those of the actual fraction. Also, the results show that the actual size of pore size smaller than the average pore sizes can be accurately measured, however, the distributon or pores larger than the average pore size is measured as it has lower rfaction than those of actual fraction of the distribution.