Various surface treatments have been applied to nearly equiatomic NiTi (Nitinol) alloys to form a protective film for bio-devices. Here, we used synchrotron-based X-ray Photoelectron Spectroscopy (XPS) to study differences in the chemical state and composition of NiTi surfaces after mechanically polishing (MP), electrochemically polishing (EP), nitric acid passivation and phosphate buffered saline (PBS) solution exposure. Our XPS results have shown that all treatments lead to the surface dominated by TiO₂ film. No significant difference in the film thickness and structure of different treated samples has been found. Mechanically polished surfaces have exhibited a higher Ni atomic concentration than the electrochemically polished surfaces in the outermost surface layer. The affects of the PBS solution on the crystal structure of mechanically and electrochemically polished NiTi samples were also examined by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. NEXAFS measurements have demonstrated all samples had similar amorphous TiO₂ film on their surfaces.