When electroni cabinet on shipboard is operatred or not, it is in various environmental conditions such as the high and low temperature, or the high temperature and humidity, therefore, the environmental test is performed to evaluate the reliability of the cabinet for these environmental conditions. However, the environmental test confirms normal operations of the cabinet for the environmental condition, and does not evaluate a corrosion of the cabinet or inner components in the cabinet. That is why a corrosion can occur if the environmental test meets conditions. Especially, when the cabinet in a non-operating state is exposed in high temperature and humidity over a long period of time, the corrosion easily occurs by condensation. To prevent the corrosion, if the cabinet on shipboard does not operate, it has the function that dehumidification is performed by an operation of heater in the cabinet and condensation does not occurs. In this study, dehumidification performance of the electronic cabinet with a heater for dehumidification was evaluated. Dehumidification performance of the electronic cabinet was predicted by performing the thermal analysis, and the validity of the analysis result was verified by a temperature test.