The anisotropy constants K1 and K2 as well as the Curie temperatures of partially iron substituted Sm2Fe17-xGax have been studied. The Sm-sublattice contribution to the magnetocrystalline anisotropy has been obtained by subtracting the Fe-sublattice contribution measured in the isostructural compound Y2Fe17-xGax. Using the linear theory of magnetocrystalline anisotropy the crystal-field parameter A20 has been calculated from K1(T) and K2(T). A20 initially decreases towards more negative values than in the parent compound, reaching -270 K a0-2 at x = 1.5, though it seems to increase slightly at higher Ga concentrations. © 1999 IOP Publishing Ltd.