Extractions were performed of the total phenolic and flavonoid contents and antioxidant properties of five edible mushroom samples—Lentinus edodes, Volvariella volvacea, Pleurotus eous, Pleurotus sajor-caju and Auricularia auricular—using three different extractants. Among the three different extractants, 50% (volume per volume; v/v) ethanol was the most suitable for antioxidant extraction from the mushroom samples. The 50% (v/v) ethanolic extract of dried L. edodes contained higher total phenolic and flavonoid contents than in the other mushroom extract samples. The antioxidant activities of 50% (v/v) ethanolic extract of dried L. edodes showed the strongest 2,2-diphenyl-1-picrylhydrazyl radical-scavenging assay (64.34%) compared to butylated hydroxyanisole (BHA) and α-tocopherol at 500 μg/mL. The ethanolic extract showed a lower reducing power of 0.10 compared to BHA and α-tocopherol at 500 μg/mL. Moreover, the L. edodes ethanolic extract also had the highest chelating ability (66.28%) which was lower than for ethylenediaminetetraacetic acid at 500 μg/mL and showed the strongest superoxide radical-scavenging activity (64.17%) compared to BHA and α-tocopherol. Therefore, the 50% (v/v) ethanolic extract of L. edodes could be used as a potential natural antioxidative source or as an ingredient in the fish and fishery product industries.