Antioxidant activities and contents of β-glucan and amino acids of wild mushrooms collected from Geosan, Boeun, Eumseong, and Bonghwa in Korea were investigated. Phaeolus schweinitzii (OK1165) displayed the highest 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (60.3%), ferric reducing antioxidant power (3.84), reducing power (1.05), nitrite scavenging activity (96.4%), total polyphenol content (54.7 mg gallic acid equivalent/g), and flavonoid content (19.98 mg quercetin equivalent/g). The β-glucan content of Pycnoporus cinnabarinus (OK1172) of 51.9% was higher than the contents of the other mushrooms. P. schweinitzii (OK1165) displayed the highest total amino acid (1,373.9 mg/kg) and essential amino acid (515.0 mg/kg) contents among the wild mushrooms. The findings confirmed that wild mushrooms could be a high-value resource for functional foods with pronounced antioxidant activity. The results also provide fundamental data for extracting useful compounds from wild mushrooms.