Provided is an artificial hair fiber which can prevent detachment between core and sheath, having superior texture close to human hair, and having superior curl retention. An artificial hair fiber has a core-sheath structure, including: a core; and a sheath covering the core; and: the core includes a core resin composition including polyester; the sheath includes a sheath resin composition including polyamide; the core and the sheath have a core/sheath mass ratio of 40/60 to 90/10; and when a melt viscosity of the polyester of the core is expressed as a, and a melt viscosity of the polyamide of the sheath is expressed as b, a viscosity ratio a/b is 0.5 to 2.5.