This study was conducted to examine the possibilities offered by sepiolite as a compatibilizing agent in the incompatible blend consisting of poly(vinylidene fluoride) and polystyrene. The effect of sepiolite on the crystalline microstructure and morphology was determined through isothermal crystallization and spherulite growth of the system under study. The effect of sepiolite on the compatibility of the system was also studied. The glass-transition temperature was determined, as well as the Flory-Huggins thermodynamic interaction parameter through two different routes : differential scanning calorimetry and inverse gas chromatography. A parallel study was conducted for the compatible system poly(vinylidene fluoride)/poly(methyl methacrylate).