The effects of the average pore size in porous glass tube membranes on the performance of the cross-flow microfiltration were investigated using oil-in-water emulsion.The flux decline with filtration time was divided into two stages. The filtration mechanism in the first stage can be explained by three types of blocking filtration models such as the complete type for pore size 0.27 mu m membrane, the intermediate type for pore size 0.75 mu m membrane and the standard type for pore size 1.47 mu m. The second stage can be also explained by the cake filtration model.The oil rejection is found to decrease with time initially, but is soon stabilized at a constant level. This was explained by the comparison among the average pore size, the pore size distribution of used membrane and the droplet distribution of the feed emulsion.The surfactant transmission of the cake filtration stage was 49% for 0.27 mu m membrane, 80% for 0.75 mu m membrane and 99% for 1.47 mu m membrane.