Talc-filled polypropylene (PP) composites were prepared by extrusion in a wide composition range (0-40 wt %). To improve the affinity relation between talc and the PP matrix, we modified the talc surface with silane coupling agents. Differential scanning calorimetry investigations on test samples, prepared by injection moulding, revealed that the talc content and its surface modification had a pronounced effect on the crystallization behavior of the filled PP composites. The experimental results indicate that a talc concentration of 2 wt % strongly affects the nonisothermal crystallization process of the PP, especially when talc is silane treated. Isothermal crystallization experiments on samples with minimum amounts of talc (2 wt %) revealed an improved nucleation activity with silane-treated talc.