In this research work, an attempt was made to study the thin film oxide formation on the dissimilar gas tungsten arc welded austenitic stainless steels of grades AISI 304 and AISI 310S using E309L filler wire. These combinations are widely used in power plant and marine applications. An assessment was carried out to estimate the metallurgical, mechanical properties of the weldment. Tensile tests revealed that the fracture occurred at the weld zone. In addition, Vickers Micro-hardness tests were performed across the length of the weldment. Furthermore, hot corrosion studies were performed on different regions (heat affected zones, weld zone and parent metal zones) of the weldment subjected to air oxidation at 600°C. It was revealed from thermogravimetric analysis that there was weight loss in the heat affected zone of the AISI 310S side after 50 cycles. The thin film oxide layer formation on various zones of the weldment was examined using the combined techniques of optical microscopy, XRD and SEM/EDAX analysis.