The thermodynamic and morphological behaviors of poly(octadecyl acrylate) (PODA) with flexible ethylene-co-vinyl acetate copolymer (EVA) with a controlled amount of vinyl acetate units in the copolymer were investigated over the entire composition region by thermal analysis, Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction, optical microscopy, and light scattering. Thermal analysis revealed that the EVA portion interferes with the side chain crystallization of PODA, as the number of crystallized methylene units in PODA was calculated from the heat of fusion of the paraffinic side chain crystals. The hexagonal packing of side chains was also confirmed by FTIR and x-ray diffraction. Optical microscope studies showed a homogeneous melt state beyond the melting temperature of EVA, but clearly showed two phases over the whole range of composition in EVA20, EVA40, and EVA50/PODA blends after the side chain crystallization of PODA. Light scattering showed the single circular halo as the evidence of phase separation when the samples were cooled to below the crystallization temperature. The changes in crystallization cannot be accounted for by the miscibility, because liquid-liquid phase separation competes with crystallization.