Abstract: A formula for the calculation of boron equivalent of impurity elements inuranium hexafluoride was deduced. The sum of boron equivalents of eightelements (Gd, B, Sm, Eu Cd, Li, Dy, Cl) which possess larger boron equivalentfactors was calculated by using experimental data. It contributes over 95% of thetotal boron equivalent of all the impurity elements (40 elements). In general,boron equivalent of above--mentioned eight elements may be used for the estima-tion of the total boron equivalent of all the impurity elements.