PURPOSE:To obtain a peptide mixture or its salt which is useful as a functional food or health food by hydrolyzing milk casein with pepsin, fractionating the hydrolysate and selecting the fraction. of specific solubility and molecular weight, having sedative action. CONSTITUTION:(A) Milk casein and (B) pepsin are added to (C) hydrochloric acid to effect hydrolysis, the reaction mixture is adjusted in its pH to 9 and combined with (D) ethanol to precipitate the subject peptide. The peptide mixture or its salt has more than 100mg/ml solubility in water, more than 1mg/ml solubility in ammonia 80% ethanol of pH9, 850 to 56,000 molecular weight, having physical condition-controlling functions.