Milk is an emulsion of butterfat globules within an aqueous solution of carbohydrates, minerals, fat droplets, and casein micelles, the latter being the largest dissolved components in milk. There are four types of casein micelles, which vary in diameter from about 100 to 200 nm[2]. The aim of this study is to measure the particle size and the zeta potential of milks, both whole and skimmed; and to investigate the influence of salt concentration on zeta potential.