We employed high-resolution 13 C cross-polarization/magic-angle-spinning/ dipolar-decoupling NMR spectroscopy to investigate the miscibility and phase behavior of poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) blends. The spinlattice relaxation times of protons in both the laboratory and rotating frames [T 1 (H) and T 1 (H), respectively] were indirectly measured through 13 C resonances. The T 1 (H) results indicate that the blends are homogeneous, at least on a scale of 200 -300 Å, confirming the miscibility of the system from a differential scanning calorimetry study in terms of the replacement of the glass-transition-temperature feature. The single decay and composition-dependent T 1 (H) values for each blend further demonstrate that the spin diffusion among all protons in the blends averages out the whole relaxation process; therefore, the blends are homogeneous on a scale of 18 -20 Å. The microcrystallinity of PVC disappears upon blending with PMMA, indicating intimate mixing of the two polymers.