Titanium alloys are widely applied in producing hard tissue implants (such as bone, joint, and teeth), but they are bioinert materials and fail to form chemical bond with host bone. Bioactive hydroxyapatite (HA) coatings can form bony contact with bone tissue and shorten the healing period, but their dissolution and fracture limit their wide application [1]. It is essential to prepare bioactively modified layer on titanium alloy with high bond strength. Microarc oxidation (MO) is a technique of ingrowing oxidation ceramic layer on nonferrous metals, which was firstly developed in 1970s [2]. The antiscuff and anticorrosion properties of titanium alloys were improved after MO treatment [3, 4]. As for biomedical application, Ca2+ and PO3− 4 ions in electrolyte could enter the ceramic layer during MO process and existed in amorphous form, so that the bioactivity potential of titanium alloys was increased [5]. But unfortunately, HA crystals were not formed on the surface of MO layer, which makes it difficult for bone tissue to attach on the implants. Hydrothermal synthesis (HS) can convert other calcium phosphates to HA [6]. Here, the MO layer containing Ca and P on Ti6Al4V was hydrothermally treated to obtain surface modified bioactive layer containing HA crystals on titanium alloy. The study also showed that the MO-HS layer has high bond strength (above 25 MPa) with biologically favorable roughness and porosity. 25 × 2.5 titanium alloy (Ti6Al4V) plates were used as substrates. They were polished with 600 and 1000# abrasive paper, ultrasonically washed with deionized water and acetone. The electrolyte was prepared by calcium salt and phosphate salt with a Ca/P mole ratio 3. Ti6Al4V plate was anode and stainless plate cathode. Pulse-direct power resource was used with voltage 350 V and occupancy/(occupancy + void) ratio 60%. The oxidation time was 3 min. The samples by MO was hydrothermally treated in an autoclave at 160, 180 for 2 or 4 h, and the pH of water was adjusted to 11–12 by adding ammonia. Scanning electron microscopy (SEM) was used to analyze the surface and profile morphology, and X-ray diffraction (XRD) and electron dispersive X-ray analysis (EDXA) were used to analyze the phase and element composition. Tensile bond strength test was carried out