A nonionic surfactant composition including: a nonionic surfactant that contains a molecule having a C10-C22 alkyl group and/or alkenyl group as a hydrophobic group, a polyoxyalkylene chain as a hydrophilic group, no aromatic ring, no C9-C14 alkyl group derived from an alcohol that is produced from a higher olefin derived from a mixture of propylene and butene through an oxo process, and no C13 alkyl group derived from an alcohol that is produced from a higher olefin derived from a propylene tetramer through an oxo process. The nonionic surfactant has a hydrodynamic radius of 5.0 to 8.0 nm at 40° C. in an aqueous solution in which a nonionic surfactant concentration is 0.1 kg/L in the nonionic surfactant composition, the radius being measured by a dynamic light scattering method.