The effect of heat treatment on the intrinsic coercivity. H-i(c) and microstructure were investigated for sintered (Nd,Dy)(15)(Fe,Co,Mo,AI)(77) Bg permanent magnet. The microstructure has been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray spectroscopy and Mossbauer spectroscopy. The observed behaviour of H-i(c) may be caused by a superposition of the following effects: (i) the distribution of the nonmagnetic phases and the ratio of the amount of hard magnetic Nd2Fe14B-phase to the amount of the residual phases; (ii) homogeneous distribution of elements in the main phases; (iii) removing the stresses in the phases; and (iv) diffusion of AI, Mo and Co into the hard magnetic Nd2Fe14B-phases.