Although magnesium (Mg) is considered as a biodegradable and biocompatible orthopedic implant, it suffers from an extremely high rate of corrosion in physiological conditions. A poly(ether imide) (PEI) has shown satisfactory corrosion protection capability as a coating for Mg with good adhesion strength; however, its innate hydrophobic property results in insufficient osteoblasts affinity and a lack of osseointegration. In this paper, we modify the physical and chemical properties of a PEI-coated Mg implant. A plasma immersion ion implantation technique is combined with DC magnetron sputtering to introduce biologically compatible tantalum (Ta) onto the surface of the PEI coating. The PEI-coating layer is not damaged during this process due to the extremely short processing time (30 s), retaining its high corrosion protection property and adhesion stability. The Ta-implanted layer (roughly 10-nm thick) on the topmost PEI surface results in long-term surface hydrophilicity as well as favorable surface conditions for pre-osteoblasts to adhere, proliferate, and differentiate. Furthermore, in a rabbit femur study, the Ta/PEI-coated Mg implant demonstrates significantly enhanced bone tissue affinity and osseointegration capability. These results indicate that Ta/PEI-coated Mg is promising with respect to achieving early mechanical fixation as well as long-term success in biodegradable orthopedic implant applications.