Mushrooms contain a variety of secondary metabolites, including various phenolic compounds, which have been shown to act as excellent antioxidants. Recently, a specific antioxidant, ergothioneine (ERG) has been identified in various genera of mushrooms, including shiitake ( Lentinula edodes). Shiitake is the second most highly consumed mushroom in the world, and present several functional properties, such as antitumor, hypocholesterolemic, antioxidant and antimicrobial potentials that have been intensively investigated. Although research was focused on its therapeutic effects, little information is available about the compounds responsible of the antioxidant properties. Our objectives were to identify changes in quality of shiitake as antioxidant source during cultivation cycles on oak woodships. The antioxidant activities and contents of potential antioxidant components, including total phenolic (TP) compounds and ERG, were analyzed in two parts of mushrooms (stipe and cap) from the successive flushes. In addition, the seasonal variations were studied. The Folin-Ciocalteu reagent was used to quantify the TP, and ERG was quantified by HPLC-DAD. The antioxidant activity was measured using the ORAC assay. Our analysis revealed only minor seasonal variations in TP and ERG contents as well as the ORAC value, excepted during the winter where these contents were 50% higher in the caps. Regarding the age of the culture, we observed a progressive decrease in the contents of TP and ERG all along the flushes, whatever the part of the mushroom. Surprisingly, the ORAC value increased in the whole mushrooms, whereas it decreased in the caps and strongly increased in the stipes. We concluded that the antioxidant activities could be largely dependent on other molecules than ERG, perhaps specific phenolic compounds. Having established the main variations in the antioxidant activity of shiitake, the chemical characteristics of the antioxidative components will be now further investigated. This study could provide valuable new opportunities for mushroom growers, since shiitake can serve as a good source of antioxidants in the human diet.