Abstract: The preparation, heat treatment and magnetic properties of light rare earth iron crystals with large and negative magnetostriction, SmFe_x（1.40＜x＜1.94）, Sm_xDy_1-yFe_y（0.84＜x＜0.92, 1.80＜y＜1.90） and Sm_0.90Dy_0.10(Fe_0.95Al_0.05)_1.80, are investigated. Two magnetostrictive maximums are observed in λ-x dependence curves of SmFe_x. The effect of phase contents on properties of Sm-Fe, Sm-Dy-Fe and Sm-Dy-Fe-Al before and after annealing is discussed. A post-process anneals is used to improve magne-tostrictive properties. The compounds SmFe₂ and （Sm, Dy）Fe₂ with huge magnetostriction propertieshave been prepared.