Disclosed are titanium oxide composite particles and a dispersion of the titanium oxide composite particles, which can improve retentivity in blood and accumulation in cancer cells while satisfactorily developing the catalytic activity of titanium oxide particles to be excited upon exposure to ultrasonic waves or ultraviolet light. The titanium oxide composite particles comprise titanium oxide particles； and a nonionic hydrophilic polymer bound to the surface of the titanium oxide particles through at least one functional group selected from carboxyl group, amino group, diol group, salicylic acid group, and phosphoric acid group. The composite particles can be rendered cytotoxic upon ultrasonic or ultraviolet irradiation to efficiently kill cells to be killed, such as cancer cells.
