The medicinal mushroom Inonotus obliquus is a traditional and widely used multi-functional fungus. Hot water (50 degrees C, 70 degrees C, and 80 degrees C) and ethanol crude extracts of L obliquus were investigated for their antioxidant activity with superoxide dismutase (SOD) and (1,1-diphenyl-2-picryhydrazyl) (DPPH) radical-scavenging activity assays. We also investigated the antiproliferative effects and ability of the extracts to induce apoptosis in human colon cancer DLD-1 cells. Among the four extracts, the ethanol extract (EE) exhibited the strongest SOD-like activity and antiproliferative effect on DLD-1 cells, and exposure to the EE resulted in the induction of apoptosis, whereas no apoptosis was observed in DLD-1 cells exposed to the hot water extracts (HWEs). HWE at 70 degrees C (HWE70) exhibited the strongest DPPH radical-scavenging activity (EC50,126 mu g/ml), whereas the EE showed the weakest activity (EC50, 224 mu g/ml). The different biological activities among the four extracts may be attributed to differences in their chemical composition, partially supported by polysaccharide, protein and phenolic content, and the H-1-NMR spectra. (C) 2008, The Society for Biotechnology, Japan. All rights reserved.