Provided are novel polyurethane elastic fibers having a high recovery stress, low hysteresis loss, and high heat resistance. The polyurethane elastic fibers of the present invention are polyurethane elastic fibers formed from a polyurethaneurea obtained from a copolyalkylene ether diol produced from different C2-10 alkylene ethers; a diisocyanate; and a diamine, the polyurethane elastic fibers being characterized in that the polyurethaneurea has a hard segment percentage of 14.0% to 25.0% as defined by formula (1): hard segment percentage (%)=(urea moiety number-average molecular weight)/{(urea moiety number-average molecular weight)+(moiety segment number-average molecular weight)}×100 (formula (1)).