Interdiffusion in Fe/Pt multilayer thin films has been studied. [Fe(1nm)/Pt(1.5nm)]20 multilayers were prepared by DC magnetron sputtering technique and subsequently annealed at temperatures of 543 - 633K in vacuum lower than 10-6 torr. X-ray diffraction (XRD) studies on these multilayer systems revealed the interdiffusion coefficients from slope of the best straight line fit of first peak intensity versus annealing time. The temperature dependence of interdiffusion in the range of 543 - 633K can be described by D=4.98×10-24 exp (0.88eV/kT) m2S-1. The coercivity, measured by Vibrating Sample Magnetometer, of the multilayer with annealing time at 603K increased, which is believed to the increase of surface roughness by interdiffusion at the interfaces of Fe and Pt multilayers, enhancement of composition gradient; and/or formation of Fe-Pt reaction phase at the interface of Fe and Pt.