Abstract: A wire for orthodontic treatment comprises an orthodontic wire made of a Co--Ni based alloy. The orthodontic wire is manufactured by subjecting it to a final cold reduction of 60 to 90%. The wire is worked into a linear shape by, for example, a mechanical straightening method, in order to correct waviness of the wire resulting from the final cold reduction. The wire is then aged at a temperature of 500.degree. through 600.degree. C. to provide an orthodontic wire which has a high mechanical strength, an excellent corrosion resistance and a superior toughness.