ABSTRACT: Total antioxidant capacity (TAC), phenolic content, and crude water-soluble polysaccharide (WSP) were determined for Lentinus edodes mycelia grown on both whey permeate (WP)-based medium with lactose content of 4.5% and controlled medium, and harvested after 5, 10, 15, or 20 d of fermentation at 25 °C. Both methanol extracts and water extracts of L. edodes in this study were found to exhibit high free radical scavenging capacity. The harvesting time was found to contribute to most of the variability in the free radical scavenging capacity. High levels of antioxidant capacities (0.28 ± 0.03 and 0.29 ± 0.06 mmol TAE/g dry weight for methanol and water extracts, respectively) were observed in mycelia grown on whey permeate and harvested on day 10. Harvesting time and the type of media can interact to alter the chemical content of mycelia. Mycelia grown in whey permeate had greater (P < 0.05) WSP than mycelia grown in the synthetic media. High levels of WSP (4.1 × 102± 71 mg polysaccharide/g dried mycelia) were found in mycelia grown in whey permeate and harvested on day 10. Whey permeate grown mycelia had phenolic compounds ranging from 4.2 ± 0.1 to 8.0 ± 0.8 mg GAE/g dried mycelia. The overall means of total phenolic contents of mycelia grown in whey permeate were 5.9 ± 0.5 and 6.2 ± 0.6 mg GAE/g dried mycelia for methanol and water extracts, respectively.