NiTi alloy was subjected to one-step hydrothermal treatment in the concentrated CaHPO4 and Ca(H2PO4)2 solutions for bioactive surface modification. The treated samples are covered by films composed of fine grains (~70 nm) and large particles (100-250 nm). XPS analysis shows that Ti at the surface presents as TiO2, Ni is not detectable, and Ca and P are in the form of calcium phosphate. X-ray diffraction peaks of anatase TiO2 and hydroxyapatite are present for the treated samples. Potentiodynamic polarization test in a Ca-free Hank’s balanced solution reveals that the treated sample has markedly improved corrosion resistance compared with the polished sample. The present work would provide a one-step bioactive surface modification method that is easily-operated, low-temperatured, less corrosive, and potentially suitable for biomedical porous NiTi alloy.