Abstract: A series of the uranium isotopic reference materials were prepared with high purity ²³⁵U and ²³⁸U. The result shows that the relative uncertainty of method of measurement is better than 0.05%. The accurate analysis of the uranium content in the reference materials is based on the potentiometric titration method. The prepared uranium isotopic reference materials can be used to recalibrate the 26 uranium standard solutions with lower uncertainty, and trace to the benchmark of potassium dichromate.