Abstract: To find out the effect of Co on magnetic properties of PrFe_10.2Mo_1.5Co_0.3 Permanent magnetic alloy, the cryatal and magnetic structures of the alloy are determined by powder neutron diffraction. Reitveld analysis of the neutron diffraction data indicates that Mo prefers the 8j site while Co prefers the 8j site. The experimental study shows that the magnetic moment and the saturation magnetization are enhanced, and the Curie temperature is raised due to the 8j crystal site Fe is replaced by Co.