High quality heterogeneous polysulfone affinity flat filter membranes having chelating groups were prepared by phase separation by the use of blends of chelating resin and polysulfone as membrane materials, N,N-dimethylacetamide as the solvent, and water as the extraction solvent. The effects of blending ratio, chelating resin grain size, and temperature of casting solution on the structure of affinity membranes were investigated. The sorption process of an affinity filter membrane for Hg2+, adsorbed under various chelating conditions such as chelating resin grain size, pH value, and the concentration of the metallic ion solution, was also studied. The results revealed that the greatest chelating capacity of an affinity filter membrane for Hg2+ was 1050 mug/cm(2) per membrane under appropriate conditions, and the sorption isotherms of Hg2+ could be expressed by the Freundlich sorption model. Dynamic chelating experiments indicated that the Hg2+ could be extracted with the affinity filter membrane and reextracted under acidic conditions.