Major milk proteins were analysed using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and two demensional (2-D) gel electrophoresis combined with isoelectic focusing(IEF). α_s- and β-caseins were recognized in acid-precipitable fractions of both Holstein (HOL) and Korean Native cattle (KNC) milk as indicated with commercial preparation of bovine caseins. κ-Casein was further identified with a positive staining of periodic acid Schiffs (PAS) reagents and disappearance of the protein after rennin treatment. Both commercial α_s-, β-and κ-casein, and our casein preparations gave albumin and β-lactoglobulin bands in the SDS-PAGE. Other unknown minor components were also found in both HOL and KNC. In 2-D analysis albumin was separated into two different spots, and β-lactoglobulin was also separated into two genetic variants, A and B. Casein complexes are highly complicated with their heterogeneity. KNC appeared to have more proteins thus sho-wing different peptide patterns. The results suggest that SDS-PAGE and 2-D gel electrophoresis would be useful to analyse the major milk proteins and are applicable to various analytical purposes.