Poly(divinylbenzene)/poly(n-butyl acrylate) core/shell latexes were investigated using solid-state C-13-NMR. The (H)T-1 rho relaxation time was found to be substantially affected by many of the seeded emulsion polymerization parameters, such as the core/shell ratio, the mode of addition of the second-stage monomer, the addition rate of the second-stage monomer, and the level of conversion of the seed latex at the time of addition of the second-stage monomer. The existence of an interphase region between the core and shell polymers was detected. Maximum interphase region thickness was achieved when the butyl acrylate was added under starved conditions. The thickness of this interphase layer was calculated to be 5-7 nm based on a model proposed by McBriety.(1) Solid-state NMR was found to be an excellent spectroscopic technique to probe the interphase region in core/shell latexes.