A precise and accurate compositional characterization methodology using wavelength dispersive X-ray fluorescence (WDXRF) spectrometry for mixed oxide nuclear fuels is reported. The methodology involves pelletization of standards and samples. The calibration plots were made by plotting the percent intensity of analyte X-ray lines against their amount percent. The relative standard deviation were 0.4% and 0.25%, respectively for uranium and thorium, having U ranging from 2.85 to 4.2 (wt%). The analytical results were compared with chemical analysis method and were in good agreement. The developed WDXRF method is non-destructive, fast and better in comparison to chemical analysis methods.