This study reports the utility of tantalum (Ta) coating for improving the surface hardness, in vitro bioactivity and biocompatibility of Co-Cr implants. The use of direct current sputtering allowed for the deposition of a dense and uniform Ta film onto a Co-Cr substrate, which was composed of beta-phase Ta grains. This hard Ta coating significantly improved the surface hardness of the Co-Cr by a factor of > 2.3. In addition, the Ta-deposited Co-Cr substrate showed a vigorous precipitation of apatite crystals on its surface after 4 weeks of immersion in simulated body fluid, suggesting its excellent in vitro bioactivity. This bioactive Ta coating led to a considerable improvement in the in vitro biocompatibility of the Co-Cr, which was assessed in terms of the attachment, proliferation and differentiation of pre-osteoblasts (MC3T3-E1). (C) 2013 Elsevier B.V. All rights reserved.