The separation and purification of bone marrow stromal cells from mixed KUSA-A1 and 9-15C cells using membrane filtration were investigated. The aim was to find the optimal membrane selection and filtration conditions for the separation of marrow stromal cells. Base membranes used for the filtration were Nylon mesh filter, sponge polyurethane (PU) porous membranes and sponge PU membranes containing 0.61% of epoxy group. After the cultivation of the mixed cells, appropriate cell concentration was prepared and the mixed or single cell solution was permeated through the membranes. High recovery ratio of 9-15C cells was obtained at the single cell concentration of 5000/ml, while permeation ratios of both 9-15C and KUSA-A1 cells were less than 3%.