We have investigated the structural and magnetic properties of Dy 2 Fe 17− x Mn x compounds (x=0–5.0) by X-ray diffraction, linear thermal expansion (LTE) and magnetization measurements. Compared with Dy 2 Co 17− x Mn x compounds for which a linear increase of the unit cell volume with increasing Mn fraction is found, the composition dependence of the unit cell volume in the Dy 2 Fe 17− x Mn x series exhibits a relative maximum around x∼0.5 before increasing monotonically for x⩾2; this behaviour can be ascribed to the existence of spontaneous volume magnetostriction as confirmed by LTE measurements. The Curie temperature (T c ) remains essentially constant (around 370K) for Mn content up to x=1 before decreasing steadily with increasing x, down to T C =232K for Dy 2 Fe 12 Mn 5 . The 3d-sublattice magnetization decreases monotonically with increasing Mn content.