An oxide sintered body is provided which does not splash from the target surface even at the time of high power film formation, has a high film formation rate, and is used in a sputtering target capable of providing a high-refractive-index film.An oxide sintered body is used which contains zinc, niobium, aluminum and oxygen as constituent elements and in which Nb/(Zn+Nb+Al)=0.076 to 0.289 and Al/(Zn+Nb+Al)=0.006 to 0.031, where Zn, Nb and Al denote contents of zinc, niobium and aluminum, respectively.