Using the precipitation contributing to turbidity of the baker's yeast hydrolysates as the object,we analyzed the precipitation's basic composition,amino acid composition,molecular weight distribution,solubility in different solvents and buffer solution of different pH,and also discussed the formation mechanisms of the precipitation.Results showed that the precipitation was mainly composed of crude protein at 62.00%,sugar totaled 28.80% and ash at 15%;the molecular weight distribution of the hydrolysates before and after the precipitation's removal showed that peptides whose molecular weight were less than 1 000 u acontributed to the precipitation's composition.Amino acid analysis revealed that hydrophobic amino acid content of the precipitation was 46%,which was higher than that of the hydrolyzate at 32.03%.Then it illustrated that the hydrophobic interaction force may be the major force to drive the precipitation's formation.The qualitative and quantitative tests of precipitation's solubility showed that the precipitation was slightly soluble in water and ammonia,and the isoelectric point of the precipitation was near pH 6.5.