The use of recycled Carbon Fibers (rCFs) into polylactic acid (PLA) matrix to produce new reinforced 3D printing filaments was assessed. Filaments containing 5 and 10 wt% of rCFs were manufactured and, in order to compare the effect of the partial oxidized surface of recycled CFs on the adhesion with PLA matrix, filaments of pure PLA and with the same concentration of washed virgin Carbon Fibers (vCFs) were also produced. As expected the addition of CFs impacts the 3D printed thermal and mechanical properties, leading to the reduction of thermal expansion up to 85% and to a substantial increase of the storage modulus up to 7.1 GPa for PLA/vCF10. Furthermore this study underlines that the use of rCFs leads to a thermo-mechanical performance well comparable with that of the analogue virgin fibers based materials, supporting the suitability of recycled CFs for 3D printing applications. Indeed, when the fiber aspect ratio is not a crucial detrimental point, the quality of recycled CFs has now achieved performances that make them a better alternative to the pristine fibers, in particular when economic aspects are also taken into account.