With focus on a higher heat-to-electricity conversion efficiency, future developments in the field of thermal energy storage are aiming at higher operational temperatures. For that, increased decomposition rates of nitrate and nitrite are the limiting factor. Until now only small-scale laboratory experiments have been performed at temperatures above 565 °C. This study presents the to our knowledge for the first-time experiment on the thermal stability of Solar Salt (60 wt-% NaNO3, 40 wt-% KNO3) at temperatures up to 600 °C with synthetic air purge gas flow in a 100 kg scale. The key to the received data is a build-in gas system with direct gas analyzer, a sample extraction system and post-analysis of salt samples, that allows determination of molten salt decomposition products. Our research provides clear evidence of the feasibility in elevating the reactor temperature to 600 °C.