Fused deposition modeling (FDM) printing of continuous fiber reinforced polymers had been a challenge until about 5 years ago. With the reinforcement of continuous fiber, the mechanical properties of FDM printed polymers are improved by leaps and bounds. In this paper, we aim to investigate the possibility of further improvement in the mechanical properties of three-dimensional (3D) printed continuous fiber reinforced polymers by adding nanoreinforcements to the polymer matrix. Kevlar fiber is selected as the continuous fiber reinforcement, nylon 6 (PA 6) is selected as the polymer matrix material, and carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs) nanoparticles are selected as the nanoreinforcements. In the experiment, CNT or GNP nanoparticles are first mixed with nylon 6 pellets to make nanocomposites, the nanocomposites are then extruded into filaments for 3D printing, and finally, both Kevlar filament and nanocomposite filament are fed through the printing nozzle and deposited on the platform. Tensile specimens are directly printed from pure PA 6 and three types of nanocomposites, namely, CNT/PA 6, GNP/PA 6, and GNP-NH2/PA 6, as well as Kevlar fiber reinforced PA 6 and three types of Kevlar fiber reinforced nanocomposites. The results indicate that although Kevlar fibers dominate the enhancement of mechanical properties for the printed composite materials, the existence of GNP nanofillers also provide a noticeable contribution to the enhancement of tensile strengths and moduli, while the effect of CNTs is much less pronounced.