Corrosion of boiler tubes at high temperature has been one of the serious issues resulting in maximum shutdown of boilers. Boiler tubes and superheaters are mainly made of stainless steel. In this paper, SS316 and Superni-718 have been used for comparative study of corrosion mechanism in actual husk-fired boiler environment. Flyash characterization has been reported in this paper along with SEM/EDS analysis of samples. XRD analysis has also been discussed to determine the phases formed on the specimens. An attempt has been made to develop a two-step corrosion mechanism for the corroded samples. The findings showed that for 800 h of boiler exposure, the minimum thickness loss of 0.29 mm was obtained for Superni-718 and so, minimum corrosion rate was also obtained for the superalloy whereas, SS316 showed an increase of 85.05% in the corrosion rate. Volatile oxides of chlorine and unprotective Fe2O3 might have been responsible for corrosion that had occurred in SS316 sample. In the case of Superni-718, formation of adherent oxides and protective CrMn2O4 might have been responsible for the high-temperature corrosion resistance. From the results, Superni-718 has proved to be more effective due to the formation of protective and adherent oxides.