The invention provides a method for preparing a peptide for improving brain function, comprising hydrolyzing milk casein with an enzymatic catalyst comprising a protease to produce a hydrolysate comprising: (i) a peptide consisting of the amino acid sequence shown in SEQ ID NO: 1 or a variant thereof (ii) a peptide consisting of the amino acid sequence shown in SEQ ID NO: 2 or a variant thereof or (iii) a mixture of the peptides of (i) and (ii), wherein the production yield of each of the peptides is 2% or more, or the total production yield of the mixture is 10% or more. The invention also provides a food or drink or a pharmaceutical composition containing the hydrolysate.本發明提供一種腦功能改善用胜肽之酵素性製造方法。具體而言,本發明提供一種腦功能改善用胜肽之製造方法、及含有該水解產物之飲食品或醫藥組合物,該腦功能改善用胜肽之製造方法之特徵在於:包括利用含有蛋白酶之酵素觸媒水解乳酪蛋白,而生成含有(i)包含序列編號1所示之胺基酸序列之胜肽或包含此胺基酸序列中缺失、置換或附加1或2個胺基酸殘基之胺基酸序列之胜肽,(ii)包含序列編號2所示之胺基酸序列之胜肽或包含此胺基酸序列中缺失、置換或附加1或2個胺基酸殘基之胺基酸序列之胜肽,或(iii)上述(i)及(ii)之胜肽之混合物的水解產物,其中,該胜肽之各自生成產率為2%以上,或該混合物之合計生成產率為10%以上。
