In this study, an optical sensor membrane was prepared for sorption and detection of cadmium(II)(Cd(II)) in aqueous solution. A polyanion, poly(sodium 4-styrenesulfonate) (PNaSS), was graftedonto the chloromethylated polysulfone (CMPSF) microporous membrane via surface-initiated ATRP.5,10,15,20-tetrakis(4-N-methylpyridyl) porphyrin p-toluenesulfonate (TMPyP) was immobilized ontothe PNaSS-grafted polysulfone (PSF-PNaSS) membrane through electrostatic interaction. The TMPyP-functionalized membrane exhibited an enhanced sorption for, and distinct color and spectral responseto cadmium(II) (Cd(II)) in aqueous solution. Larger immobilization capacity of TMPyP on the membraneled to stronger sorption for Cd(II), and smaller one made the optical sensor have a faster (in minutes) andmore sensitive response to the ion. The detection limit study indicated that the functional membranewith proper amount of TMPyP (