Protein fractionation using ultrafiltration is feasible after extensive process optimization, yet the poor selectivity of membranes is still one of the critical factors limiting the application of membrane systems to protein fractionation. Our present work on protein fractionation uses sandwich ultrafiltration membranes by exploiting the membrane pore size and the pore distribution characteristics of the membranes. The aim is to improve the selectivity of the separation by achieving a pure protein product in the permeate from a binary protein mixture. Two membranes of similar or different MWCO combination (30, 50 and 100 kDa) are stacked together in various sandwich arrangements. The proteins with molecular weight between 10 and 70 kDa (Lysozyme, Myoglobin and BSA) are used as model proteins in single and binary mixtures. The observed transmissions of Lysozyme with sandwich of the same membrane of 30/30, 50/50, and 100/100 kDa are 78, 85 and 97%, respectively; and these values are comparable to the transmission for the respective single membrane, being consistently slightly lower. Similar trends are being found for BSA.