Resistance switching phenomena in an amorphous Ni-Ti-O film were investigated. Very clear bipolar resistive switching characteristics were observed with good reproducibility. Stable retention and on/off pulse switching operation was demonstrated. An analysis of x-ray photoelectron spectroscopy of the Ni-Ti-O film provided a clue that the observed unusual bipolar resistance switching in the film is due to a microscopic change in the Ni-O and Ti-O binding states at the Ni-Ti-O film/electrode interface.