In this study, morphology changes and bone formation on plasma electrolytic oxidation (PEO)-treated Ti-6Al-4V alloy in electrolyte containing Ca, P, Sr, and Si ions were researched using various experimental instruments. Ti-6Al-4V ELI disk was used as the specimens. The specimen was used as the anode and the carbon rod as the cathode. Pulsed DC power of 280 V was applied to all specimens for 3 min. at 25 degrees. The electrolyte used for PEO was produced by mixing up Ca(CH3COO)(2)center dot H2O, C3H7NaCaO6P, Sr(CH3COO)(2)center dot 0.5H(2)O, and Na2SiO3 center dot 9H(2)O. To investigate the bioactivity, PEO-coated specimens and untreated Ti-6Al-4V specimens were immersed in simulated body fluid (SBF) for 12 h at 36.5 degrees. The phase and surface morphology of the specimen were analyzed by a thin film X-ray diffractometer, field-emission scanning electron microscopy, Energy dispersive X-ray spectroscopy, and surface roughness tester. The pore size decreased, while the number of pores increased, as the content of Sr increased. In the case of the amount of 5Si addition, the size of the pores decreased whereas the number of pores increased as the content of Sr increased. Ca, P, Sr, and Si ions were uniformly distributed on the surface and, in the case of Sr and Si addition, the contents of Ca, P, and Sr significantly increased. The cell proliferation and bone-like apatite increased as the content of Sr and Si. (C) 2017 Elsevier B.V. All rights reserved.