Optimum operating conditions of a molten salt oxidation (MSO) reactor system were determined based on the results of trial destruction tests of spent cation exchange resins doped with radioactive metal surrogates(Co, Cs, Sr). The organic destruction performance was tested by changing the MSO reactor temperature from 750°C to 950°C and the excess air rate from 50% to 150%. The efficiency of organic destruction was substantial at the temperatures of 850°C or higher and the excess air ratio of 100% or more. Based on the result of partitioning test of the radioactive metal surrogates in the MSO reactor system, the optimum operating temperatures of the primary MSO reactor was determined to be 850oC. A further increase in the salt temperature resulted in a significant vaporization of semi-volatile radioactive metal species, cesium.