Novel narrow distributed nanospheres with polystyrene shells and cross-linked poly(methacrylamide) (polyMMA) cores were fabricated. The cross-linking of the poly(p-nitrophenyl methacrylate) (polyNPMA) cores of micelles, formed by the self-assembly of well-defined block copolymer (poly(styrene-b-p-nitrophenyl methacrylate) (poly(St-b-NPMA))) in chloroform, was realized in the solutions directly through the reaction with ethylenediamine instead of in films as in other cases reported [3,8-11]. Further substitution of p-nitrophenol units with ammonia produced polyMMA cores. Dynamic light scattering was used to monitor the self-assembly process of poly(St-b-NPMA) in chloroform, the effects of the cross-linking and amino-substitution of the polyNPMA cores on the morphologies of the micelles, meanwhile, the changes in the chemical structures were verified by FTIR.