Neutron diffraction patterns have been obtained for polycrystalline Y3Fe5-xMnxO12 at 300 K. The fraction of octahedral sites occupied by Mn3+ has been found to be 0.72 for x=0.05 and 1 for x=0.09. The magnetic moments of tetrahedral sites and octahedral sites have been determined respectively for x=0.05 and 0.09. The observed magnetic scattering is consistent with the Neel model and the measured saturation moment.Magnetizations were measured as a function of applied magnetic field from 800 Oe to 10 kOe in the range of 1.5-300 K. Magnetic anisotropy were determined from the approach to saturation, |k1| was found to decrease with Mn3+ content.