ITER diagnostic lower ports will be used to exchange divertor cassettes and install diagnostic systems. Invessel components of diagnostic lower port #02 (LP#02) will be mounted on a divertor cassette and a support structure, so-called a diagnostic rack, to be removed and reinstalled collectively. Japan Domestic Agency is responsible for procurements of an integration engineering of LP#02 and a divertor impurity monitor, a main tenant system in LP#02. This paper presents preliminary thermal analyses for two critical components in LP#02, the diagnostic rack and a mirror box on the divertor cassette, which will be exposed to the harsh thermal load from plasma. Realistic fabrication methods for cooling the diagnostic rack and a required cooling path layout of the mirror box on the divertor cassette have been assessed to implement the preliminary design from the viewpoint of thermal analysis.