We measured the antioxidant activity of human, rat, bovine, rabbit, and guinea pig albumins against the superoxide, hydroxyl, and 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radicals. The albumins of different animal species did not differ in antioxidant activity against superoxide. Human and rat albumins exhibited antioxidant activity against hydroxyl radicals, but bovine, rabbit, and guinea pig albumins showed weaker antioxidant activity than human and rat albumins. Human, rat, rabbit, and guinea pig albumins, but not bovine albumin, exhibited strong antioxidant activity against DPPH radicals. Human and rat albumins with strong antioxidant activity against hydroxyl radicals contained methionine-123 in domain 1, but bovine, rabbit, and guinea pig albumins did not. Rat, rabbit, and guinea pig albumins with strong antioxidant activity against DPPH radicals had methionine-264 in domain 2. Human albumin did not have methionine-264, but methionine-298 and methionine-329 in domain 2. Bovine albumin, with the weakest antioxidant activity against DPPH radicals, contained no methionine residues in domain 2. These results suggest that methionine residues in domain 1 or 2 influence the antioxidant activity of albumin.