In the present research, mechanical properties of a conventional carbon/epoxy composite were improved via incorporating reinforced polyacrylonitrile (PAN) nanofibers between the carbon fabric layers. Alumina (Al2O3) nanoparticles were employed to improve mechanical properties of the PAN nanofibers. Morphological studies of the nanofibers by scanning electron microscopy (SEM) showed increasing the alumina nanoparticles (more than 1 wt%) leading to nanoparticle agglomeration. However, the transmission electron microscopy (TEM) confirmed no alumina agglomeration occurred at 1 wt%, which the highest mechanical properties of the nanofibers was achieved for this nanoparticle content. Statistical analysis of the obtained both in-plane and out-of-plane mechanical properties on hybrid composites (carbon/epoxy composite containing nanofibers) showed that the composite reinforced with Al2O3-PAN nanofibers had greater mechanical properties rather than that of control composite (without the nanofibers) even the hybrid composite containing the same amount of neat PAN nanofibers. Al2O3-PAN nanofiber reinforced composite improved their neat PAN counterparts in tensile strength and flexural strength by 8 and 7%, respectively. Furthermore, Compared to the control composite the enhancements resulting from the Al2O3-PAN nanofibers incorporation were obtained at 23 and 20%, for tensile and flexural strength, respectively.