Novel micro-porous membranes made of whey protein isolate (WPI) were developed. Aggregates of WPI comprised the bulk of the membrane, the size and packing density of which were varied by changing CaCl2 concentration (0.3-0.05 M) and WPI concentration (30-40 wt.%), respectively. Aggregate sizes of the membranes made with 0.3, 0.1, 0.05 M CaCl2 were roughly 1.5, 1, and 0.8 mum, respectively. Skin layer of thickness about 0.5 mum was found on either side of the membrane, but the thickness could reach 5 mum at 0.3 M CaCl2. Additionally, the porosity of the skin layer was shown to be modifiable with the addition of surfactant. Membranes were stable in hexane with flux values on the order of 1-1000 gal/ft(2) d depending on the morphology of the membrane. A discussion concerning the formation and use of protein gel as a membrane is included.