The role of spatial and electron structure, hydrophobic properties and concentration of organoselenium compounds on their interaction with fungal metabolites--extracellular lectins of Lentinula edodes (shiitake mushroom) has been considered. By the hybrid method of density functional theory at the B3LYP/6-31G(d,p) theory level, spatial and electronic structure of the 1,5-diphenyl-3-selenopentanedione-1,5 (preparation DAPS-25), 1,5-di(4-methoxyphenyl)-3-selenopentanedione-1,5 and 1,5-di(4-ethoxyphenyl)-3-selenopentanedione-1,5 molecules has been studied. The above molecules have been stated to be substantially similar to each other by their electronic and spatial characteristics. By means of the QSAR properties evaluation by the atomic-additive schemes, it has been shown that the molecules of the preparation DAPS-25, its dimethoxy- and diethoxy-substituted are close to each other by the hydrophilic-lipophilic balance, whereas di-n-octoxy derivative DAPS-25 is explicitly hydrophobic. The hemagglutinating activity of lectins in the presence of the preparation DAPS-25 and its alkyloxy-substituted increases, therewith the most effective addition is 1,5-di(4-ethoxyphenyl)-3-selenopentanedione-1,5. Apparently, the greater effectiveness of the said substance compared to DAPS -25 is caused by the formation of hydrogen bonds with a participation of unshared electron pairs of oxygen atoms from the ethoxy groups and mobile hydrogen atoms from the OH groups of glycoconjugates on erythrocytes surface. The positive effect of 1,5-di(4-n-octoxyphenyl)-3-selenopentanedione-1,5 is not so prominent, since the enlarged alkyl chain shields the aromatic fragments of organoselenium molecule participating in the binding with lectin.