[Problem] To provide a polyurethane elastic yarn which has the high strength and ductility sought in polyurethane elastic yarn, and also has excellent durability and heat resistance, as well as little fatigue at low temperature; and a production method thereof.[Means of Resolution] A polyurethane elastic yarn made from polyurethane which has polymer diol and diisocyanate as starting substances, wherein said polyurethane comprises a polyurethane A containing a polybutadiene structure in which the proportion of 1,2-bonded butadiene structure to 1,4-bonded butadiene structure in the molecule is in the range from 91:9 to 20:80.