The isothermal section of the phase diagram of the ternary system Dy-Mn-Ni system at 803 Kwas investigated by powder X-ray diffraction (XRD), differential thermal analysis (DTA), optical microanalysis and electron probe microanalysis techniques. It consists of 13 single-phase regions, 22 two-phase regions and 10 three-phase regions. At 803 K, the maximum solid solubilities of Mn in Ni, Dy2Ni17, DyNi5, Dy2Ni7, DyNi3, DyNi, Dy3Ni2 and Dy3Ni are about 31at.% Mn, 6 at.% Mn, 5.5 at.% Mn, 3 at.% Mn, 5 at% Mn, 5 at.% Mn, 3 at.% Mn and 1.5 at.% Mn, respectively. The maximum solid solubilities of Ni in Mn, DyMn12 and Dy6Mn23 are about 2.6 at.% Ni, 2 at.% Ni and 4 at.% Ni, respectively. DyMn2 and DyNi2 form a continous solid solution in this system. The binary compounds DyNi4 and Dy4Ni17 were not observed in this work. The existence of any ternary compound was not observed. (C) 2002 Published by Elsevier Science B.V.