An object of the present invention is to provide a composition for forming an organic semiconductor film that is excellent in printing properties and makes is possible to prepare an organic thin film transistor excellent in mobility and insulation reliability. Another object of the present invention is to provide an organic thin film transistor, electronic paper, and a display device. The composition for forming an organic semiconductor film of the present invention contains an organic semiconductor material, a phenolic reductant, a polymer compound having a weight-average molecular weight of equal to or greater than 500,000, a surfactant, and an organic solvent having a standard boiling point of equal to or higher than 150° C., in which a ratio of a content of the organic semiconductor material to a content of the polymer compound is 0.02 to 10 based on mass, and a ratio of a content of the phenolic reductant to the content of the polymer compound is 0.1 to 5 based on mass.