Magnetostriction of amorphous Sm-Fe and Sm-Fe-B thin films is systematically investigated over a wide composition range from 14.1 to 71.7at% Sm. In the case of Sm-Fe-B thin films, the amount of B is varied from 0.3 to 0.8at%. Good magnetostrictive characteristics, particularly at low magnetic fields, are achieved in both Sm-Fe and Sm-Fe-B thin films, although better properties are observed in B containing Sm-Fe thin films. At a magnetic field of 100Oe, for example, the magnitude of magnetostriction is -350 ppm in a Sm-Fe thin film and it is -470ppm in a B containing Sm-Fe thin film. With their excellent magnetostrictive characteristics, the present Sm-Fe and Sm-Fe-B thin films are considered to be suitable for Si based microdevices.