Rare earth iron garnets R3Fe5-x Mn x O12(R=Pr,Nd,Sm,Eu) were prepared through mild hydrothermal method.The initial alkalinity of solutions was thought to play an important role in governing the content of Mn.The effect of substitution Fe3+ ions by Mn3+ ions on magnetic properties was investigated.The saturation magnetizations of Mn-doped samples are larger than that of corresponding parent compounds due to the moment of Mn3+ ion being smaller than that of Fe3+.It is clearly shown that incorporation of Mn3+ gives rise to significant variations in the Curie temperature.With increasing of Mn content x,Curie temperatures reduced sharply for the garnets,which could be explained by the exchange interaction between a-d Fe3+ being reduced in these compounds. Rare earth iron garnets R3Fe5-xMnxO12 (R = Pr, Nd, Sm, Eu) were prepared through mild hydrothermal method. The initial alkalinity of solutions was thought to play an important role in governing the content of Mn. The effect of The substitution of Fe3 + ions by Mn3 + ions on magnetic properties was investigated. The saturation magnetizations of Mn-doped samples are larger than that of corresponding parent compounds due to the moment of Mn3 + ion being smaller than that of Fe3 +. It is clearly shown that incorporation of Mn3 + gives rise to significant variations in the Curie temperature. With increasing of Mn content x, Curie temperatures reduced sharply for the garnets, which could be explained by the exchange interaction between ad Fe3 + being reduced in these compounds.