A capillary zone electrophoretic method is described for the determination of a caseinoglycomacropeptide. The optimized conditions employed a poly(vinyl alcohol)-coated capillary and 50 mM phosphate buffer at pH 2.5 to enable baseline separation of several glycoforms. The method was validated and performance was good in terms of precision (both peak area and migration time), selectivity, linearity, and accuracy. The method was used to determine caseinoglycomacropeptide (2%w/w) in a cosmetic lotion. The validated method was finally used to monitor the stability of this caseinoglycomacropeptide in the cosmetic lotion over a period of four months.