Abstract:The effects of exogenous Se on the topography and quantitative characters of Agaricus brasiliensis S. Wasser fruit bodies were studied under scanning electronic microscope (SEM). When exogenous Se was 30 mg kg-1, the length, width and number of spores of Agaricus brasiliensis S. Wasser increased by 20.92％, 5.41％ and 114.13％, respectively, and had significant difference (P<0.01) to the control. When treated with 10 and 20 mg kg-1 Se, the maximum and minimum diameters and number of the cystidium increased by 34.78％ and 7.73%, 13.40％ and 15.26％, 27.78％ and 33.33％ (P<0.01), respectively, and the minimum width of the mycelium increased by 45.90％ and 50.82％ (P<0.01), respectively. The morphological structures of the spore, cystidium and mycelium varied under SEM.