The efficiency of a hydrophobic cross-linked polyzwitterionic acid for the simultaneous removal of Co(II) and organic dyes from water was examined. The synthesis of the resin was conducted via cyclotetrapolymerization of N,N-diallyl-N-aminomethylphosphonic acid as a hydrophilic monomer, N,N-diallyl-N-octadecylammonium chloride as a hydrophobic monomer, and SO2 in the presence of a cross-linker using the initiator a,a'-azoisobutyronitrile. The efficiency of the resin for the removal of Co(II) was evaluated under the effects of metal ion concentration, temperature, adsorption contact time, and medium pH. The results show the adsorption data fitted a pseudo-second-order model. The standard enthalpy change Delta H degrees was 23.2 kJ/mol, suggesting an endothermic adsorption process. The adsorption from the mixture of the binary systems of Co(II) with eriochrome Black T, methyl orange, phenol, or methylene blue exhibited a distinct bimodal behavior that could be ascribed to the chelating and hydrophobic nature of the prepared resin. The resin, by virtue of having the advantages of high capacity and good ability to adsorb Co(II) ions and organic contaminants simultaneously, is indeed a promising candidate for water purification.