DESIGN ANALYSIS ON OPERATING PARAMETER OF OUTLET TEMPERATURE AND VOID FRACTION IN RDE STEAM GENERATOR.HTGR is one of the next generation reactor types. HTGR is currently considered as one of the leading reactors for the future nuclear power plant. The steam generator is one of the main components in HTGR as well as in RDE. In the steam generator, the heat is transferred by high temperature helium gas in the shell side to water in the tube side to generate the superheated steam. The purpose of this work is to design the operating parameter of outlet temperature and void fraction of steam based on feed water mass flow rate and inlet temperature variations in RDE steam generator. In this work, the ChemCAD program was used. Both inlet and outlet temperature of helium gas have been set up as boundary conditions. The result shows that using the mass flow rate of 4.3 kg/s -4.8 kg/s and water inlet temperature of 110 o C -160 o C, the superheated steam outlet temperature (void fraction = 1.0) is obtained in the range of 275.5 o C -600 o C. This analysis is beneficial to assess 10 MW RDE design especially in the steam generator system operating parameters.