Abstract: An improved polyurethane-urea elastic fiber is obtained by incorporating a specific urea compound prepared by reacting the following compounds together: (a) a nitrogen-containing compound having both at least one bifunctional amine group selected from a group consisting of a primary amine group and a secondary amine group and at least one nitrogen-containing group selected from a group consisting of a tertiary nitrogen group and a heterocyclic nitrogen group; (b) an organic diisocyanate; and (c) at least one compound selected from the group consisting of a mono- or di-alkylmonoamine, an alkylmonoalcohol and an organic monoisocyanate. With the incorporation of the specific urea compound, the polyurethane-urea elastic fiber which can be fast dyed exhibits enhanced thermosettability and increased elastic functions can be produced through a stabilized spinning process.