Abstract: An object of the present invention is to provide: an oxide semiconductor thin film which is produced at relatively low cost and has a high carrier mobility and a high resistance to light stress when used for forming a thin film transistor; and a thin film transistor formed using the oxide semiconductor thin film. The oxide semiconductor thin film contains In, Zn, and Fe, wherein, with respect to a total number of In atoms, Zn atoms, and Fe atoms, a number of In atoms accounts for greater than or equal to 20 atm % and less than or equal to 89 atm %, a number of Zn atoms accounts for greater than or equal to 10 atm % and less than or equal to 79 atm %, and a number of Fe atoms accounts for greater than or equal to 0.2 atm % and less than or equal to 2 atm %. The present invention involves a thin film transistor including the oxide semiconductor thin film.