Y3MnxFe4.85-xO12 (x=0, 0.02, 0.04, 0.06, 0.08 and 0.1) garnet ferrites (YMnlG) were prepared by conventional solid-state reaction method in air atmosphere. The effect of Mn addition on the microstmcture and electromagnetic properties of YIG were investigated by means of techniques such as X-ray diffraction, scanning electron microscopey, network analyzer, hysteresigraph, magnetic balance and electron paramagnetic resonance spectrometry. Pure garnet phase of Y3Fe5O12 was identified for all the samples, except for minor YFeO3 phase appearing in the sample with x=0.06. The addition of Mn showed little influence on the dielectric constant of YIG, which varied between 14.2 and 14.5. Substituting Mnn+ for Fen+ in YIG decreased the total amount of Fe ions, inhibited the reduction of Fe3+ and promoted the grain growth of garnet phase, which led to the decrease in dielectric loss and coercivity. Because the amount of Mn3+ ions in octahedral sites increased with Mn concentration, the saturation magnetization showed a slight decrease firstly and then increased notably. The addition of Mn could also increase the renanence ratio of YIG ferrites by decreasing the magnetostriction constant λ111. Therefore, doping Mn into YIG ferrites with proper quantity could improve electromagnetic properties of YIG significantly. The YMnIG ferrite with x=0.08, i.e., Y3Mn0.08 Fe4.77O12, showed the optimum electromagnetic properties: εr=14.2, tanбe=l.5× 10-4, Hc=36 A/m, 4πMs= 192 mT, Br/Bs=0.84, ΔH=6.8 KA/m.