The use of natural fibers as fillers in polymer matrix composites is an alternative for reusing the fruit wastes that originated from the food industry. This work aimed to evaluate the effect of grape skin fiber (GSF) on the rheological and mechanical properties of polypropylene/GSF (PP/GSF) composites. The composites were prepared by extrusion followed by injection molding and characterized by rheological, morphological, and mechanical properties. Rheological measurement results showed an increase in viscosity at low frequencies. The relaxation time of the PP/GSF composites increased by about 415% with the increase in the GSF content from 1 to 3 phr. Capillary rheometry results indicated that the processability of PP was not compromised with the addition of GSF. Morphology analysis by scanning electron microscopy (SEM) indicated a good interaction between the PP matrix and GSF and a good dispersion/distribution of the fibers in the PP matrix. The impact strength decreased by about 14 and 17% with the addition of 1 and 3 phr, respectively, of GSF to PP whereas the elastic modulus remained almost unchanged.