The fracture behavior of injection-molded polypropylene (PP) composites reinforced with hybrid short glass fibers (SGF) and short carbon fibers (SCF) was studied. The fracture toughness ( K c) of the composites was measured using compact tension specimens made from the manufactured plaques. It was of interest to note that the fracture toughness of hybrid SGF/SCF/PP composites was higher than that predicted by the rule of hybrid mixtures (RoHM), showing a positive hybrid (synergistic) effect. Also, the fracture toughness of the hybrid composites was higher than that of both single SGF/PP and SCF/PP composites, thus showing that the synergistic effect was remarkable. SEM observations on the fracture surfaces of the materials were performed. A three-layer structure, that is, a skin–core–skin layer structure, of the composites was observed for all the investigated composites. For the single short-fiber composites, the three-layer structure was the same as that reported previously. In the skin layers, the fibers lay parallel to the mold flow direction (MFD); in the core layer, the fibers were perpendicular to the MFD. However, for the hybrid short-fiber composites, the three-layer structure was different. In the skin layers, the fibers were aligned parallel to the MFD, but in the core layer, the fibers were aligned oblique to the MFD. The oblique fibers would result in a higher pullout toughness contribution to the hybrid composites. Moreover, for the single SCF/PP composite, the matrix in the core layer fractured in a brittle fashion. In contrast, for the hybrid SGF/SCF/PP composites, the matrix in the core layer fractured in a ductile manner, imparting an additional contribution to the total toughness of the hybrid composites. Consequently, the positive hybrid (synergistic) effect on the fracture toughness of hybrid SGF/SCF/PP composites could be explained.