Abstract Graft copolymerization of poly(acrylonitrile) onto sodium alginate was carried out in aqueous medium using potassium persulphate as an initiator. The effects of pH, time, monomer concentration, initiator concentration, temperature, and backbone concentration were investigated. Percent grafting and grafting efficiency were evaluated. Isolation of graft copolymer from unreacted sodium alginate was carried out using the selective solvent extraction technique. FTIR and thermogravimetric analysis for poly(acrylonitrile), sodium alginate, and sodium alginate-graft-poly(acrylonitrile) were studied to establish the occurrence of grafting. A probable mechanism for grafting is proposed.