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UO2(NO3)2 and UF4 are significant intermediates that connect different chemical unit operations (such as dissolution, evaporation, concentration, extraction and etc.) in uranium chemical industry. Commonly, there is a basic physicochemical question about phase equilibrium of ternary systems UO2(NO3)2 + HNO3 + H2O and UF4 + HF + H2O, it is crucial to understand the phase behavior and thermodynamic properties of them with the continuous development of uranium chemical industry. In this study, solid-liquid phase equilibria of ternary systems UO2(NO3)2 + HNO3 + H2O and UF4 + HF + H2O at 298 K were studied by means of isothermal dissolution method, the solubilities and densities of equilibria liquid phase were investigated experimentally for two systems, the composition of equilibria solid phase of system UO2(NO3)2 + HNO3 + H2O at 298 K were determined by Scherinemakers’ wet residue method, and the method of X-ray diffraction was used to determine the composition of equilibria solid phase for system UF4 + HF + H2O at 298 K. Phase diagrams and diagrams of density-composition were constructed for systems UO2(NO3)2 + HNO3 + H2O and UF4 + HF + H2O at 298 K. Results show that there are unique isothermal dissolution curve for two ternary systems, and corresponding crystallization zone are UO2(NO3)2·6H2O and UF4·2.5H2O, respectively.