The magnetocrystalline anisotropy and the spin reorientation of Sm1-xDyxFe10.5Mo1.5 were investigated in detail. At room temperature, all Sm1-xDyxFe10.5Mo1.5 alloys possess easy c-axis anisotropy and the magnetocrystalline anisotropy field decreases with increasing Dy concentration. However, at low temperature, a spin reorientation transition of axis-to-cone type was observed in the Sm1-xDyxFe10.5Mo1.5 alloys with x ≥ 0.8. The spin reorientation temperatures increase with increasing Dy concentration in the Sm1-xDyxFe10.5Mo1.5 alloys. © 1999 Kluwer Academic Publishers.