Provided is a sputtering target of sintered Ti-Nb based oxide, wherein the sputtering target consists of titanium (Ti), niobium (Nb), and remainder being oxygen and unavoidable impurities, and the atomic ratio of Ti and Nb is 0.39 ‰¦ (Nb/(Ti + Nb)) ‰¦ 0.79. The sputtering target of sintered Ti-Nb based oxide has a high refractive index and a low extinction coefficient. Also provided is a thin film of Ti-Nb based oxide obtained by using the foregoing target, which enables high-rate deposition. The thin films has superior transmittance, is subject to minimal reduction and variation of reflectivity, and is useful as an interference film or a protective film of an optical information recording medium, or as a part of a constituent layer of an optical recording medium. The thin film can also be applied to a glass substrate; that is, it can be used as a heat reflecting film, an antireflection films or an interference filter,