The Bi3+ and Mn4+ doped on nanopowders of Yttrium Iron Garnet (YIG) Y3-xBixFe5-xMnxO12 (x = 0, 0.1, 0.2, 0.3, 0.5) by mechanochemical method was prepared. The experimental optimum time for ball milling was 15 h. The structural and magnetic properties of Y3-xBixFe5-xMnxO12 were investigated. XRD patterns reveal that the structures of nanopowders are bcc and the garnet phase has been obtained after calcination at 1100 °C for 3 h. The shift of diffraction lines to smaller angles shows the lattice constant of the samples increased with increasing Bi3+ and Mn4+ concentration. TEM image showed particle crystal size of 40 nm. It showed that magnetization of nanopowders increases with increase in cations concentration value and then decreases. In addition, the Curie temperature (Tc) of samples decreases with increasing Bi3+ and Mn4+ concentrations, which can be discussed by decreasing the number of super exchange interaction.