Abstract: The data of molar volumes of uranous nitrate and nitric acid are necessaryfor the calculation of the changes in phase volume during the extraction inU(NO_3)_4--HNO_3/30%TBP--kerosene system. However, the data of the partial molar volume of U (NO_3)_4 are not available in literature. In the present work, the molar volumes of U (NO_3)_4 and HNO_3 are calulatedby linear fitting of the experimental data. The result of the molar volume ofHNO_3 is consistent with those in literature.