Sm₂Fe_l7N_X permanent magnet was prepared by using Sm_2.0-2.5Fe₁₇ alloy powders as the starting material, and the effect of starting composition of alloy powder on nitriding process and magnetic properties was investigated. The alloy powders were subjected to mechanically grinding (MG) in NH₃ atmosphere for 10.8ks and subsequent nitriding in N₂ gas flow for 3.6-10.8ks at as low temperature as 623K. X in Sm₂Fe₁₇N_X was confirmed to be about 3 for all of specimens after nitriding for 7 10.8ks. Maximum coercivity, 960kA/m (12.1kOc) was observed for Sm 2.3 specimen after the above nitriding process, and even the Sm=2.0 specimen with stoichiometric composition showed the coercivity higher than 80OkA/m (10kOc).