Vacuum membrane distillation (VMD) process received a great deal of attention by many investigators because of its promising applications in many separation areas. Theoretical models published in literature describe vapor flux through membrane pores ignoring membrane pore space interconnectivity. Those models, in most cases are restricted to Knudsen type of flow and in a less extent to the combined Knudsen-viscous mechanism also described by the dusty gas model. This paper is one of a series of papers in which a Monte Carlo simulation model is developed to describe the vapor flux across the membrane in association with membrane distillation process. Unlike earlier paper in the series, this paper deals with VMD for the first time. The membrane pore space is described by a three-dimensional network of interconnected cylindrical pores, having a pore size distribution. The model can take into account all related mass transport mechanisms based on the kinetic theory of gases. When this model was applied to VMD process, it was assumed that water vapor is the only permeant, the VMD process is in an isothermal condition and there is no surface effect. The effects of the bulk feed temperature, downstream pressure and membrane pore size on the simulated VMD flux were discussed. The Monte Carlo model predictions were found to be in qualitative agreement with available experimental data when Knudsen type of flow was considered. When viscous type of flow is considered, the simulation results indicate that the higher feed solution temperature and higher pore size do not necessarily increase the vapor flux.