The graft copolymerization of the vinyl monomers that were prepared by reactions of methyl acrylate and 4-aminoazobenzene derivatives, such as 4-aminoazobenzene, 4-amino-4'-methyl azobenzene, 4-amino-4'-nitro azobenzene, and 4-amino-3',5'-dinitro azobenzene, onto potato starch were carried out by the initiation of potassium persulfate. The evidence of grafted copolymers was investigated by using FTIR spectroscopy and acid hydrolysis technique. The relationship between grafting efficiency and monomer structure as well as polarity was studied. The experimental results showed that the graft copolymerization is independent of the polarity of the vinyl monomers and that the structures of monomers exhibit a marked influence on the graft copolymerization, namely, the larger the substitute is, the lower the grafting efficiency will be.