摘要：The late lactation stage milk (LL milk) and normall latation stage milk ( milk) were collected from dairy herd of ititute ranch for study on their protei and fats. The protein content of LL milk was different from milk showed utable and wave form like variation during lactation period. The amino acid composition of LL milk was different to that of milk. The liquid chromatographes and SDS gel electrophoresis patter showed the serum protein of both LL and milk were similar in components but different in content ratio. The SDS gel electrophoresis of casein micelles showed some different bands between them. The amino acid compositio of their casein micelle were quite similar. Short of hydrophobic amino acid residue in fat membrane protein of LL milk could be a possible reason for causing utable globular fat and difficulty to separate cream by centrifuging. Gas chromatographic analysis and infrared spectrometric measurement revealed fat of LL milk contained more of short chain fatty acid C6 to C16. It is possible reason why cream separated from LL milk became so soft and poor in yield as compared with milk.