In this study, novel biomedical Co29Cr9W3Cu samples were fabricated using selective laser melting (SLM) technology. In order to better understand the formation of the lattice defects during the melting process, and the tensile deformation mechanism of the SLM-produced Co29Cr9W3Cu samples, the microstructures of the samples before and after tensile deformation were observed using a scanning electron microscope (SEM), a transmission electron microscope (TEM), and an electron back-scattered diffraction (EBSD), respectively. The SEM morphology indicated that the non-equilibrium structure of the SLM-produced Co29Cr9W3Cu samples contained cellular and columnar subgrains. The TEM observation and EBSD analysis showed that the accumulated residual stress during the SLM process predominated in the overlapping regions between the adjacent scanning tracks, which consequently induced a larger number of the lattice defects, such as dislocations and overlapping stacking faults. The analysis of the tensile deformation revealed that the main plastic deformation was caused by the strain-induced martensitic transformation effect in the SLM-produced Co29Cr9W3Cu samples.