The suitability of polysulfone ultrafiltration membranes (UFM) designed for commercial water treatment has been investigated for separation of protein (PR) from sweet whey. Ultrafiltration (UF) of whey originated from dairy has been realized by a self-made pilot plant, which has been in service for about one year. The influence of two whey temperatures (9 and 30 °C) on the efficiency of protein concentration has been examined. Application of investigated UF elements gave whey protein concentrate (WPC) with 5 to 6 times excess amount of protein content compared to the initial. At the same time, the prevalent content of lactose was removed to permeate. Better results were obtained with cold whey filtration. Besides the fact that the molecular weight cutoff (MWCO) of the investigated membranes was 50-100 kDa, the results showed very successful concentrating of whey proteins of dominantly lower molar weights than 50-100 kDa. Investigated membranes are beneficial for design and construction of UF plants for exploitation in small dairies.