Propylene-carbon monoxide (P-CO) alternating copolymer was blended with poly(methyl methacrylate) (PMMA) by solution precipitation. Various aspects of blend behaviors were studied by using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), dynamic dielectric thermal analysis (DETA), Fourier transform infrared (FTIR) spectroscopy, and solid-state cross-polarization magic angle spinning (CP-MAS) NMR The blends exhibited single T-g’s at all compositions, which is an indication of miscibility on the scale of 100 Angstrom. In addition to the alpha-relaxation (glass transition),the beta-relaxation of P-CO was detected by DETA at -65 degrees C. The LR absorptions of the carbonyl groups of P-CO and PMMA were located at 1706 and 1730 cm(-1), respectively. The intensities of both bands were normalized by correcting concentration variation; their ratio changed with blend composition, consistent with some specific interactions involving one or both carbonyl groups. The solid-state NMR proton spin-lattice relaxations in both the laboratory and rotating frame were single-exponential processes. The result showed intimate mixing between P-CO and PMMA on a scale of <30 Angstrom.