The present invention provides elastic polyurethane yarns which possess excellent elongation, recoverability, heat resistance and chemical resistance, as well as a method of manufacturing the same. The elastic polyurethane yarns comprise a polyurethane being composed mainly of a polymeric diol and a diisocyanate, and contains through incorporation a compound having within the molecule a phosphorus-nitrogen interatomic bond(s). The process can produce the elastic polyurethane yarns by adding to a solution of the polyurethane a compound having within the molecule a phosphorus-nitrogen interatomic bond(s), followed by spinning.