Apatite-forming ability on a zirconia surface was investigated using a conventional SBF (c-SBF), a 1.4 SBF (concentration of ions 1.4 times higher than in SBF) and a supersaturated Ca/P solution. After 5 days a small amount of hydroxyapatite was formed on the zirconia surface in the 1.4 SBF, whereas no apatite was detected on the zirconia surface exposed to the c-SBF for 5 days. In the supersaturated Ca/P solution some isolated clusters of hydroxyapatite were observed on the zirconia surface after only 2 hours, and after 27 hours of immersion time, the zirconia surface was homogeneously covered with hydroxyapatite. Some of the covered zirconia substrates were heat treated at 1050°C for 1 hour. The thermally treated and untreated samples were immersed in SBF for 7 and 14 days. The results confirmed that additional hydroxyapatite was formed in the SBF in both cases, regardless of whether the covered zirconia substrate was pre-heated or not.