This experiment was carried out to study on the protein composition of casein micelles. Casein micelles were isolated by different temperature of ultracentrifugation. And the composition of individual caseins fur the fractions was determined by DEAF - cellulose column chromatography, The results are summarized as follows: 1. When skimmilk was centrifuged at 4℃, 8.5℃, 13.5℃, 18℃ and 30℃ for 60 min at 200,000 x g, the values for the sedimented casein micelles were 57.80%, 79.79%, 80.85%, 90.43% and 86.88% respectively. 2. When skimmilk was centrifuged for 60 min at 100,000 x g, the values for the sedimented casein micelles and serum casein were 60.85%, and 39.15% at 20℃ and 40.24% and 59.76% at 4℃. 3. The relative amount of αs-, β-, k- and γ-caseins in serum casein which was not sedimented by centrifugation for 60 min at 100,000 x g was 44%, 29%, 19% and 8% at 20℃ and 38%, 34%, 16% and 12% at 4℃ respectively.