In spite of the interesting properties of cellulose nanocrystals (CNCs), such as abundance in nature, biodegradability, low density, high strength, etc., its application as reinforcing agent in polymer nanocomposites remains limited to only a few hydrophilic polymers such as poly vinyl alcohol (PVOH) and poly ethylene oxide (PEO). Strong inter-particle interactions due to hydrogen bonds lead CNCs to form agglomerates when it is introduced into nonpolar matrices. Consequently due to a lack of strong interface between the matrix and substrate, achieving enhanced mechanical properties with more widespread polymers such as hydrophobic polyolefins is challenging. Thus, compatibilization is a key issue to improve the properties of CNCs-hydrophobic polymer composites. In this work, rheological and mechanical properties of polypropylene (PP)/CNCs nanocomposites were compared with those of nanocomposites containing poly(ethylene-co-vinyl alcohol) as a compatibilizer. The nanocomposites were prepared by a Brabender internal mixer at CNC content of 3 and 5 wt%. The compression molded nanocomposite dog-bones and disks were characterized regarding their tensile and dynamic rheological behavior, respectively. The complex viscosity and storage modulus of the nanocomposites samples with compatibilizer were increased, particularly at low frequencies, compared to the non-compatibilized nanocomposite samples. Young’s modulus and tensile strength of the nanocomposite samples containing the compatibilizer were increased up to ca. 37% and 15%, respectively compared to the neat PP. The elongation at break was decreased in all PP/CNCs nanocomposite samples, but less for the nanocomposite samples containing the compatibilizer. The crystallinity of the PP of the nanocomposites and also the crystallization temperature were increased after compatibilization. These results could be ascribed to the efficiency of the poly(ethylene-co-vinyl alcohol) as a compatibilizer that favors a better dispersion and wetting of hydrophilic CNCs within the hydrophobic PP. Keywords: cellulose nanocrystals, polypropylene, compatibilization, poly(ethylene-co-vinyl alcohol), mechanical properties