This study aimed to determine the free radical scavenging and antioxidant potential of hot water extracts prepared from different combinations and ratios of submerged cultivated mycelial biomass of medicinal mushrooms. Total phenolic compounds, flavonoid content, and antioxidant activity were evaluated for combined crude hot water extracts from medicinal higher Basidiomycetes mushrooms belonging to ten genera. The results demonstrate that almost all tested combinations were good sources of phenolic compounds and flavonoids, ranging between 16.42 and 18.83 gallic acid equivalents/g and 1.5 and 4.34 mg rutin equivalents/g, respectively. Moreover, free radical scavenging properties were evaluated with the DPPH and ABTS assays and metal chelating effects were investigated. All tested samples and/or extracts demonstrated significant free radical scavenging properties and antioxidant potential.