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Sm2Fe17-xNbxNy (x = 0-4) powder was synthesized by HDDR treatment and nitrogenation. The effects of partial Nb substitution for Fe on the structural and magnetic properties of Sm2Fe17-xNbx alloys and their nitrides were investigated.It was seen that Sm2(Fe,Nb)17 phase exists in both annealed and HDDR-treated Sm2Fe17-xNbx alloys. However, its content is decreased with the increase in Nb substitution. In annealed alloys, Sm2(Fe,Nb)17 phase becomes unstable and will dissociate into SmFe2 and Fe-rich phases when x ＞ 1.5. With HDDR-treatment, the Nb concentration in recombined Sm2(Fe,Nb)17phase is decreased, and the content of Fe-rich phases is increased. Sm2Fe17-xNbx powder exhibits dendritic cracks and fine particles with a size of less than 300 nm. In nitrogenated alloys, N atoms mainly enter 2:17-type phase to form Sm2(Fe,Nb)17Ny. Partial Nb atoms in Sm2(Fe,Nb)17Ny phase will be released or excluded by nitrogen atoms. Fe-rich phases increase, and are followed by the amorphous Sm2(Fe,Nb)17Nyphase. Nb substitution for Fe with x = 0.5 and 1.0 in Sm2Fe17-xNbxNypowders increases the coercivity and remanence. But when x is greater than 2.0, Nb substitution will deteriorate the magnetic properties.