Tacrine is the first drug licensed for the treatment of Alzheimer disease. Unfortunately, reversible hepatotoxicity limits its clinical use. In our previous study, we found that tacrine induced apoptosis in HepG2 cells by reactive oxygen species (ROS) formation and mitochondria dysfunction. Inonotus obliquus is a mushroom traditionally used as a folk medicine in Asia. In this study, the possible protective effect of polysaccharides from I. obliquus was investigated. The results showed that I. obliquus polysaccharides (IOP) reduced tacrine-induced apoptosis in HepG2 cells. Inhibition of tacrine-induced ROS generation, 8-OHdG formation in mitochondrial DNA, and loss of the mitochondrial transmembrane potential by IOP were also observed. Furthermore, IOP decreased the cytochrome c release and activation of caspase-3 induced by tacrine. These data suggest that IOP could inhibit tacrine-induced apoptosis in HepG2 cells. The protection is mediated by an antioxidant protective mechanism. Consumption of IOP may be a plausible way to prevent tacrine-induced hepatotoxicity.