Gas chromatography/mass spectrometry (GC–MS) were used to characterize the polysaccharides in Agaricus brasiliensis. GC–MS analysis showed that the A. brasiliensis polysaccharide was a typical heteropolysaccharide and mainly composed of glucose, arabinose and mannose in the molar percentages of 78.38%, 10.46% and 8.51%, respectively. The Fourier-transform infrared spectra (FT-IR) of A. brasiliensis polysaccharides revealed typical characteristics of polysaccharides. The samples had the characteristics of hydroxyl groups, C–H band and α-pyranoses. Ischemia–reperfusion treatment markedly decreased myocardial SOD activity and increased MDA level in rats treated with ischemia–reperfusion. Pharmacological experiment showed that administration of A. brasiliensis polysaccharide could significantly enhance myocardial SOD activity and reduce MDA level in rats treated with ischemia–reperfusion. At the same time, administration of A. brasiliensis polysaccharide could still significantly reduce (p<0.01) caspase-3 level in rats’ brain. Results indicated that A. brasiliensis polysaccharide was beneficial in some cardiovascular diseases.