An object of the present invention is to provide a
polyurethane urea elastic fiber whose physical properties do not change much over time and which retains its initial mechanical properties, and a method for obtaining this
fiber by modifying the molecular chain and ends of the
polyurethane urea polymer. Another object of the present invention is to provide a
polyurethane urea elastic fiber whose use can improve
inventory management and
fiber processing condition management, and which can be used to obtain a fabric with stable physical properties and qualities, and to provide a method for producing this
fiber. The present invention is a polyurethane urea
elastic fiber comprising: polyurethane urea
polymer A having a molecular chain using a
polymer diol, a diisocyanate, and an organic amine as starting materials, and having a primary or secondary amino group on at least one end; and polyurethane urea polymer B using a polymer
diol, a diisocyanate, an organic amine, and an organic
carboxylic acid as starting materials, and containing an
amide bond, wherein the polyurethane urea elastic fiber contains primary or secondary amino end groups in the range of 0.1 meq or more and 20 meq or less per
kilogram of polyurethane urea elastic fiber.