This experiment was carried out to compare some properties of casein micelles in Korean native cattle`s milk with those of Holstein cow`s milk. Casein micelles in size were fractionated by ultracentrifugation, and the individual caseins in casein micelles were fractionated by DEAE-cellulose column chromatography. The results obtained were summarized as follows; 1. The total protein contents of Korean cattle`s and Holstein cow`s milks were 4.17% and 3.24%, respectively, and the casein contents of them were 3.27% and 2.57%, respectively. 2. When casein micelles in Korean cattle`s and Holstein cow`s milks were sedimented by centrifugation at 100,000g for 60min, the ratio of micellar casein and serum casein(non-sedimented casein) of the former was similar to that of the latter. However, the relative amount of casein micelles in Korean cattle`s milk precipitated by centrifugation at 100,000g for 10 min was a little lower than that of Holstein cow`s milk. On the other hand, the relative amounts of casein micelles in the former precipitated by centrifugation at 100,000g for 30 and 60min were relatively higher than those in the latter. 3. The relative amount of k-casein in Korean cattle`s milk was slightly higher than that of Holstein cow`s milk, but the amounts of α_s-casein and β-casein of the former were nearly the same with those of the latter. 4. By rennet action, the amount of NPN released from casein of Korean cattle`s milk showed a slightly higher value than that of Holstein cow`s milk, and during the rennet action for 60 min, 5.6% and 3.4% of NPN of the total nitrogen content were released from the former and the latter, respectively. It was, however, observed that there was no difference between both of them on the gel electrophoresis.