Solid-state reactions in layered Sm/Fe powder particles with an overall composition of SM12Fe88, obtained by ball milling, have been investigated by X-ray diffraction. During annealing at 500-degrees-C, one reaction, Sm+2Fe --> SmFe2 was observed in the time-range studied. However, during annealing at 800-degrees-C, five reactions were observed : Sm + 2Fe --> SmFe2, Sm + 3Fe --> SmFe3, 2Sm + 17Fe --> Sm2Fe17, 2SmFe2 + 13Fe --> Sm2Fe17, and 2SmFe3 + 11Fe --> Sm2Fe17. It is proposed that such reactions occur by a nucleation and growth process. Reactions of samarium with iron can be governed by nucleation; Sm/Fe interfaces possessing a higher free energy per unit area can play an important role in the nucleation. The observed results are discussed.