To provide polyurethane elastic yarn improved in heat-setting properties, especially, the polyurethane elastic yarn improved in the heat-setting properties and having excellent performance suitably used for pantyhose.

This polyurethane elastic yarn improved in the heat-setting properties is obtained by reacting an intermediate polymer having isocyante end groups with an organic diamine and an organic monoamine to form a segmentalized polyurethane and then spinning the segmentalized polyurethane, wherein the reaction is conducted by setting a ratio of the organic diamine to the organic monoamine and another ratio of total amine groups to the isocyanate end groups to specific ranges, respectively.