Poly(methyl methacrylate)-graft-polystyrene was prepared by radical copolymerization of methyl methacrylate and methacryloyloxyethyl polystyrene macromonomer. By means of H-1 n.m.r. spectroscopy and static light scattering (SLS), molecular weight distribution (MWD) and chemical composition distribution (CCD) were investigated for as-polymerized samples and their fractions separated by size exclusion. All fractionated samples had approximately the same chemical composition as those of the unfractionated copolymers. Apparent molecular weight measured by SLS was dependent upon solvent. The following conclusions were deduced from these results : the as-polymerized copolymers had polydispersities in CCD and MWD that were not correlated with each other. In contrast with the as-polymerized samples, the size-exclusion-fractionated samples showed a strong CCD-MWD correlation, while the two-dimensional distribution functions of CCD and MWD for all fractions were similar to each other. In view of the fact that the chain dimension of a long-branched polymer decreases with increasing branch density at the same molecular weight, the present results were consistently explicable.