An object of the invention is to provide a nanofiber having excellent uniformity of the fiber diameter and capable of giving a satisfactory external appearance in a case in which the nanofiber is used to produce a nonwoven fabric, and a nonwoven fabric produced using the nanofiber. The nanofiber of the invention is a nanofiber containing a cellulose acylate having a degree of substitution of from 2.75 to 2.95.