To explore the possible usefulness of ${eta}$-glucans as natural antioxidants, the antioxidant profiles of ${eta}$-glucan, extracted from Saccharomyces cerevisiae KCTC 7911, and water soluble and insoluble mutant ${eta}$-glucan, isolated from yeast mutant S. cerevisiae IS2, were examined by five different in vitro evaluation methods: lipid peroxidation value (POV), nitric oxide (NO), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, reducing power, and ${eta}$-carotene diffusion assay. The antioxidant activities of all ${eta}$-glucans evaluated in POV test were comparable to or better than that of the known antioxidant, vitamin C. Remarkably, the ${eta}$-glucan and water insoluble mutant ${eta}$-glucan possessed 2.5-fold more potent activity than vitamin C at a dosage of 2 mg. Although vitamin C showed 100-fold greater activity than all ${eta}$-glucans in NO and DPPH tests for measuring the radical scavenging capacity, all ${eta}$-glucans revealed higher radical scavenging activity than the known radical scavenger, N-acetyl-L-cysteine (NAC), in DPPH test. The water insoluble mutant ${eta}$-glucan had 2.6- and 5-fold greater antioxidative activity than water soluble ${eta}$-glucan in NO and DPPH tests, respectively, showing that all ${eta}$-glucans were able to scavenge radicals such as NO or DPPH. While all ${eta}$-glucans revealed lower antioxidant profiles than vitamin C in both reducing power activity and ${eta}$-carotene agar diffusion assay, the ${eta}$-glucan and water insoluble mutant ${eta}$-glucan did show a marginal reducing power activity as well as a considerable ${eta}$-carotene agar diffusion activity. These results confirmed the potential usefulness of these ${eta}$-glucans as natural antioxidants.