Ultrafiltration (UF) is an important process in the food industry, particularly for dairy applications such as concentration of milk. The major problem in membrane separation process is decline in flux over time of operation. This flux decline is attributed to the fouling of membrane. Membrane fouling is affected by three major factors, namely, the membrane material properties, the feed characteristics and the operating pressure. Two models of UF process (resistance and diffusion) were developed to predict the permeate and retentate fluxes decline during concentration of milk as a function of time under different transmembrane pressures. Experiments were carried out to study the effect of different transmembrane pressures on the permeate and retentate fluxes. Also, milk concentration was determined with time at different pressures. Flux recovery during cleaning cycle was also recorded. The experimental results were used to validate the model results. The experimental results were compared with the predicted data and they were in a good agreement with each other.