Ganoderma is a well-known medicinal macrofungal genus, of which several species have been thoroughly studied from the medicinal perspective, but most species are rarely involved in. In this study, we focus on the polysaccharides extracted from Ganoderma boninense and their antioxidant activity. Ganoderma boninense is a serious pathogen of oil palms that are cultivated commercially in Southeast Asia. Response surface methodology was conducted to optimize the liquid medium composition, and the mycelia biomass reached 7.063 g/L, that is, 1.4-fold compared with the seed medium. The crude and purified polysaccharides extracted from the fermentation broth showed well 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical scavenging abilities, and the scavenging abilities of purified polysaccharides reached 94.47 % and 99.88 %, respectively. Six fractions of polysaccharides were extracted and purified from fruiting bodies, mycelia and fermentation broth separately with the elution buffers of distilled water and 0.1 M NaCl solution. Generally, the polysaccharides from fruiting bodies showed stronger protective effect on H2O2-induced HepG2 cell oxidative damage than other fractions. A total of five to seven monosaccharides were identified in the six fractions of polysaccharides. The correlation analysis revealed that the content of fucose was significantly correlated with the antioxidant activity of polysaccharides, while xylose showed negative correlation results. In summary, the polysaccharides from G. boninense have a potential to be used as natural antioxidants.