The growth of interest in additive manufacturing has brought a significant development to this technology. Fused Deposition Modeling® (FDM®) is one of the most well know processes for polymer materials. The mechanical properties of a FDM® 3D printed sample is related to the adhesion force between each printed layer and to the presence of voids between there is inherent for this process. These questions are related to the rheological characteristic of the polymer, since lower viscosity implies in a higher filling of the voids with molten polymer, increasing the contact area between the layers, improving the interfacial adhesion. In this study, a FDM® printer was used to calculate the applied shear rate at the nozzle of the printer. It was found that the range of shear rate applied to the material is between 1,000 and 1,500 s-1. The rheological characteristics of commercially available filaments of poly(lactic acid) (PLA) and acrylonitrile-butadiene-styrene (ABS) were evaluated in a parallel plate and in a capillary rheometer. Comparing the calculated shear rate with the rheological curve, it was found that both materials are well described by the Power Law viscosity model. Test specimens for tensile and flexural mechanical properties were printed in eight different conditions of filling pattern, filling density and printing direction. The mechanical properties obtained for printed specimens were compared with those obtained for injected specimens. It was found that the flexural and tensile properties from samples printed on-edge with 70% of rectangular filling were very close (at least 90%) from those obtained for injected samples. The results can be explained by the macromechanics theory developed for composites: the printed filaments responding together to the mechanical stress can perform similarly or better than the continuous material in the injected samples, despite the presence of the voids in the printed samples. Acknowledgements: FAPESP (2018/03266-5)