Polyphenol-rich fraction from edible mushroom, Russula albonigra, was tested for total phenol, flavonoid, β-carotene, lycopene and ascorbic acid and in vitro antioxidant activity in terms of DPPH radical scavenging and chelating effect of ferrous ion, reducing power and total antioxidant capacity assay. Findings showed that EC50 values were below 1 mg/ml except reducing power test. The extract exhibited 50% reducing power at only 1.2 mg/ml concentration. Estimated putative antioxidant components are in order of phenol > flavonoids > β-carotene > ascorbic acid > lycopene. Results imply that R. albonigra can be a potential source of natural antioxidant which may be used as food supplement to treat various oxidative stress related diseases.