Ceramic microfiltration (MF) membranes were used to separate serum proteins (SP) from casein (CN) micelles in skim milk. The impact of skim milk soluble calcium and lactose concentrations, retentate flow channel geometry (round or diamond-shaped), uniform transmembrane pressure (UTP), and retentate flow channel diameter (4 mm or 6 mm) on factors that impact MF process efficiency (SP removal, limiting flux (LF), and limiting retentate protein concentration (LRPC)) were determined. Skim milk LF (91 kg[MIDDLE DOT]m-2[MIDDLE DOT]h-1) was lower than milk protein concentrate with added lactose (MPC+L) LF (124 kg[MIDDLE DOT]m-2[MIDDLE DOT]h-1) due to a reduction in calcium. MPC+L LF was lower than milk protein concentrate (MPC) LF (137 kg[MIDDLE DOT]m-2[MIDDLE DOT]h-1) due to the higher viscosity contributed by lactose. No differences in SP removal were detected among the 3 feeds below the LF. Feeding a MF system with MPC instead of skim milk will reduce the membrane surface area required to process a given volume of milk. Performance of membranes with round and diamond flow channels was compared in UTP mode. Performance of the membrane with round flow channels was compared with and without UTP. Using UTP increased LF by 5%, but SP removal was not affected. Using round instead of diamond channel membranes increased LF by 24%. The 47% increase in membrane area per unit volume of the diamond channel system resulted in its higher (19%) modular permeate removal rate. Using membranes with diamond channels could reduce some of the costs associated with ceramic MF of skim milk if fewer membrane modules could be used. Retentate flow channel diameter did not affect the LRPC at constant cross-flow velocity. At a given longitudinal pressure drop, 6 mm membranes could achieve a higher cross-flow velocity and, thus, a higher LRPC than 4 mm membranes. The higher LRPC of 6 mm membranes might facilitate 95% SP removal in 2 MF stages. 4 mm membranes require 21% more energy than 6 mm membranes to remove a given amount of permeate. Using 6 mm membranes would be advantageous for processors wishing to reduce energy costs or maximize protein concentrations in MF retentates.