[Problem] An object of the present invention is to provide a polyurethane elastic fiber with excellent textile properties and textile property stability over time by including in the polyurethane elastic fiber a specific polyurethane having in the molecular structure a salt structure in which specific functional groups are ionically bonded to each other, and to provide a method for producing such a polyurethane elastic fiber. Another object of the present invention is to provide a polyurethane elastic fiber that allows for easier inventory control and processing condition management of fibers when used, and that can be used to obtain fabrics with stable fabric properties and fabric quality, and to provide a method for producing such a polyurethane elastic fiber. [Solution] A polyurethane elastic fiber comprising polyurethane A and additive B below. Polyurethane A: A polyurethane using as starting materials a polymer diol, a diisocyanate, and a chain extender, and not having a tertiary amine in the skeleton. Additive B: A polyurethane or polyurea using as starting materials a diol and/or a diamine and a diisocyanate, and having a tertiary amine nitrogen bonded only to a non-aromatic carbon in the skeleton, the tertiary amine nitrogen bonding ionically to a sulfonic acid compound to form a sulfonic acid amine.