In this study, optimization of operating condition of two in-series UF 6 separator condensers in UCF unit was performed. Modeling and simulation of two condensers was performed in other project seperatly.In order to use that model for optimization, the modelimprovedfor prediction of theof mist conditions.These two shell and tube condensers were modeled via control volumes with finite length in axial direction of input gases. The equations of mass, energy and momentum balance were written for each of the condensers. Comparison of the modeling predictions with Isfahan UCF industrial data in regard to important variables indicated a very good compatibility. The average error between the modeling and industrial data for the first and second condenser were calculated to be 1.39 and 2.24%, respectively. Finally effect of input water temperature and input gas velocity on convective heat transfer coefficient, condensed layer thickness, condenser efficiency, the amount of condensed UF 6 and the amount of produced mist were investigated. The obtained results indicated that by increasing water temperature up to 283 K, the amount of condensed UF 6 increased and subsequent higher temperature led to the reduction of condensed UF 6 . The increase of input water temperature reduced the amount of mist and condenser efficiency. The increase of input gas velocity led to the reduction of the amount of mist and the enhancement of the convective heat transfer coefficient, condenser efficiency and the condensed layer thickness. Finally, the analysis of the effective variables via the developed modeling computer software revealed that the optimal temperature of cooling water and the input gas velocity are 10 ?C and 0.09 m/s, respectively. Key Words Uranium hexafluoride, Condensation, Condenser, Optimization