From the comparative biochemical viewpoint the author studied the transamination of 16 different α-amino acids, 4 of ω-amino acids, di-amino acids, cysteic acid and α-ketoglutaric acid in the brain of common turtle (Clemmys japonica); and obtained the following results: 1. When compared with the brains of catfish and mice the brain of common turtle reveals generally a lower transaminase activity, especially it is markedly low in the case of alanine, leucine, valine, norvaline, tyrodine, γ-aminobutyric acid, and cysteic acid. 2. The same as in the case of the brain of catfish no transaminase activity of phenylalanine can be observed in the brain of common turtle; and also methionine and glycine are not transaminated just as in the mouse brain. 3. In the brain of common turtle β-alanine is not at all transaminated. 4. Arginine shows the transaminase activity in the brain of common turtle.