Solid-state NMR spin diffusion measurements have been used to investigate the local structures in two miscible polymer systems, the isotopic polystyrene blend PS-d(5)/PS-d(3) and poly(2,6-dimethylphenylene oxide)(PPO)/PS-d(3). The experimental spin diffusion build-up curves were compared with theoretical ones based on a number of structural models. It was found that a Gaussian correlation model furnished the best agreement with the experimental data, and this implies the existence of some short-range ordering in the local environment in such nominally miscible blend systems. The best fit of the spin diffusion curves gave a correlation length of 0.5-0.6 nm for the PS-d(5)/PS-d(3) blends and 0.4 nm for the PPO/PS-d(3) blends. The correlation lengths for the PS-d(5)/PS-d(3) blends were found to be independent of the blend compositions. The result also suggests that the concentration fluctuation in a 50/50 PPO/PS-d(3) blend is weaker than that in a 50/50 PS-d(5)/PS-d(3) blend, indicating a molecular interaction less favorable to homogeneity in the latter.