Due to the presence of numerous bioactive compounds, including polysaccharides and polyphenols, mushroom-based food supplements are claimed to have many beneficial health effects. Despite their popularity, concerns have been raised in recent years over the quality of mushroom products, particularly regarding their non-standardized chemical composition. In this study, the ?-glucan and total phenolic contents, as well as the antioxidant potential of mushroom-derived supplements available on the Serbian market were analyzed. The obtained results, revealing considerable differences in ?-glucan and total polyphenol contents among these products, reflect variations in mushroom species, forms and recommended dosing regimens. A correlation between the total phenolic content and antioxidant activity was observed. The presence of other active ingredients, such as vitamin C, has contributed to antioxidant variability among the analyzed products. The obtained results indicate the need for the standardization of mushroom-derived food supplements to ensure their claiming effects.