Abstract: Graft copolymerization of styrene. (St) onto humic acid (HA), using H₂O₂-FeCl₂ redox system as initiator in DMOSmedium was investigated.It was found that HA had distinct inhibiting and retarding effect on the polymerization of St,and the ratio of H₂O₂-FeCl₂ was an important factor influencing the graft copolymerization.With increase of the H₂O₂-FeCl₂ ratio,the rate of polymerization increased,while the grafting cfficiency decreased, the grafting degree approched a maximal value when the H₂O₂-FeCl₂ ratio was 3(mol/mol).The grafting efficiency and grafting degree increased with increase of polymerization temperature The ratio of St to HA also had a direct influence on the grafting efficiency and grafting degree but not on the grafting ratio. The appearance of a new adsorption band (1120cm^-1) in the IR spectrum of copolymer was attributed to C-O-C link formed in the HA-g-PSt molecule during the polymerization. The product obtained by further sulfonation of graft copolymer is readily Soluble in water, acid and alkalisolution.