The reversion in magnesium binary alloys with rare-earth metals (Nd, Sm, Y, Gd, Tb, Dy, Ho) at a temperature of 300ºC has been studied. The phenomenon of the reverse dissolution of rare-earth metals in solid magnesium has been established to begin in all alloys under study already after short-term annealing at 300°C for 15 min. As the annealing time at 300°C further increases, the reverse dissolution of rare-earth metals in solid magnesium first continues and then the magnesium solid solution becomes again depleted of rareearth metals because of their precipitation. The degree of reversion has been found to generally increase with an increase in the atomic
number of the yttrium-group rare-earth metal in accordance with its position in the lanthanum row: Gd, Tb, Dy, and Ho. The degree of reversion in the alloys with cerium-group metals (Nd, Sm) with atomic numbers below those of Gd, Tb, Dy, and Ho is substantially smaller than that is in the alloys with yttrium-group metals.