Solid state NMR was successfully used to determine the proton spin-lattice relaxation time in the rotating frame (T 1 ρH) for systems based on polypropylene (PP) and PP with titanium dioxide (TiO 2 ) organically modified or unmodified incorporated, in order to understand the molecular behavior of these systems. These techniques were employed in the samples organically modified and unmodified TiO 2 to investigate the effect of organic modification on the dispersion and distribution of the particles in the PP matrix. The results were analyzed in terms of the effect of the particles organic modified or not according to the intermolecular interaction in the composites. According to the T 1 ρH values, all composites showed at least two domains: the short values were related to the rigid part, which included the crystalline and amorphous phase constricted in it, while the longer times were attributed to the amorphous region, which had higher molecular mobility compared to the rigid region of the materials. The increase in the relaxation time parameter in the composites compared to the pure PP was associated to the strong interaction between titanium dioxide particles and the polymer chains. This effect was more pronounced for the systems containing organically modified TiO2. According to the results, it could be inferred that intermolecular interaction occurred in the CH 2 and CH groups, being more intense with CH 2 groups. Finally, the solid state NMR techniques were able to evaluate the molecular dynamics of those systems.