Polymer blends and complexes prepared from poly(methacrylic acid) (PMAA) and poly(4-vinylpyridine) (P4VPy) were investigated by differential scanning calorimetry (DSC) and high-resolution solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy. Complexes were obtained from ethanol/water (1:1) solutions, whereas blends were cast from dimethylformamide (DMF) solutions. Each of the complexes and blends showed one composition-de pendent glass transition temperature (T-g), indicating that both the complexes and the blends are homogeneous on a scale of 10-30 nm. Furthermore, the T-g value of a complex is much higher than that of a blend with the same composition. Measurements of the proton spin-lattice relaxation time in the rotating frame, T-1 rho(H), reveal that each of the complexes and blends has one composition-dependent T-1 rho(H), indicating that both the complexes and the blends are homogeneous on a scale of 1-3 urn. However, the calculated domain sizes of the complexes and blends are almost the same.