Fruiting bodies of some wild and cultivatable mushrooms contain medicinal compounds which are being used in traditional medicines and cosmetics. Champignon mushroom (Agaricus bisporus) is the most widely cultivated species of edible mushroom worldwide. This paper focuses on antioxidant and antimicrobial importance of A bisporus. Water-soluble polysaccharide-enriched fraction was isolated from the dry carpophores of Agaricus bisporus. Antioxidant activities were investigated using in vitro assay systems: 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and chelating ability on ferrous ions. Antimicrobial activity was tested against Gram positive and Gram negative bacteria in vitro by disk diffusion method in order to determine the zones of inhibition. At concentrations of 0.1-10 mg/ml, the scavenging abilities of A bisporus ranged between 12.3-75.5 %. The radical scavenging ability of the positive controls-tocopherol and ascorbic acid, at the concentrations of 0.1-20 mg/ml, were between 79.9-80.8 and 80.6-91.1 %, respectively. Polysaccharide extract from A bisporus showed steadily increasing chelating ability as concentrations increased to 88.2 % at 20 mg/ml. The chelating ability of the citric acid was between 7.2-10.7 %, at the concentrations of 0.1-20 mg/ml. The study of antimicrobial potential of polysaccharide extract showed more potent activity against Gram-positive Enterococcus faecalis ATCC 49532 (26.7 ± 0.2 mm), Bacillus cereus 10876 (27.5 ± 0.4 mm), Geobacillus stearothermophylus ATCC 7953 (22.8 ± 0.3 mm) than Gram-negative bacteria Pseudomonas aeruginosa ATCC 35032 (10.4 ± 0.6 mm), Proteus hauseri ATCC 13315 (12.1 ± 0.1 mm) Escherichia coli (0157:H7) 35150 (12.7 ± 0.4 mm) with exception of Klebsiella pneumoniae ATCC 27736 (22.3 ± 0.2 mm)
