Optical microscopy, differential scanning calorimetry, and small angle Xray scattering techniques were used to study the influence of crystallization conditions on the morphology and thermal behavior of samples of ternary blends constituted of isotactic polypropylene (iPP), atactic polymethylmethacrylate (aPMMA), and a novel graft copolymer of unsaturated propylene with methylmethacrylate (uPP-g-PMMA). The purpose was to assess the uPP-g-PMMA capability to act as compatibilizer for iPP/aPMMA materials. It was shown that the presence of uPP-g-PMMA copolymer affects the interfacial tension between the iPP and aPMMA phase in the melt state, the aPMMA particle size, and particle-size distribution is modified. After complete crystallization of the iPP phase at relatively low undercooling, in a range of crystallization temperatures, the presence of the uPP-g-PMMA phase was found to modify both mode and state of dispersion of minor component and spherulitic texture and inner structure of spherulites fibrillae. The extent of the induced modifications was dependent on a combination of composition and undercooling. Also, relevant thermodynamic parameters of the iPP phase, such as the equilibrium melting temperature and the surface free energy of folding, were strongly affected by the presence of the uPP-g-PMMA phase, opposite effects being observed depending on the uPP-g-PMMA content. The observed melting temperature and surface free energy of folding values were accounted for by the growth of iPP lamellar crystals with different perfection, thickness, and surface disorder.