A target for sputtering which enables to attain high rate film-formation of a transparent conductive film suitable for a blue LED or a solar cell, and a noduleless film-formation, an oxide sintered body most suitable for obtaining the same, and a production method thereof.A oxide sintered body comprising an indium oxide and a cerium oxide, and further comprising, as an oxide, one or more kinds of an metal element (M element) selected from the metal element group consisting of titanium, zirconium, hafnium, molybdenum and tungsten, wherein the cerium content is 0.3 to 9% by atom, as an atomicity ratio of Ce/(In+Ce+M) , the M element content is equal to or lower than 1% by atom, as an atomicity ratio of M/(In+Ce+M) , and the total content of cerium and the M element is equal to or lower than 9% by atom, as an atomicity ratio of (Ce+M)/(In+Ce+M) , characterized in that said oxide sintered body has an In2O3 phase of a bixbyite structure as a main crystal phase, has a CeO2 phase of a fluorite-type structure finely dispersed as crystal grains having an average particle diameter of equal to or smaller than 3 μm, as a second phase; a production method for a oxide sintered body obtained by mixing indium oxide powder and cerium oxide powder, and the raw material powder with average particle diameter of equal to or smaller than 1.5 μm containing oxide powder of M element and then molding the mixed powder, and sintering the molding by a normal pressure sintering method, or molding and sintering the mixed powder by a hot press method, and the like.