In the present paper, an attempt has been made to discuss the degradation mechanism of bond coat and bond coat/top coat interface in thermal barrier coating system in the presence of corrosive salts such Na2SO4 and V2O5.These salts come from impurities in low grade fuel used in gas turbine industry. Salt mixture of Na2SO4 + V2O5 was prepared and applied on surface of thermal barrier coating (TBC) specimens. The specimens were exposed isothermally to 900oC for 200, 400 and 700 hours. SEM analysis revealed the formation of thermally grown oxide (TGO) in specimens sprayed with corrosive salts. Results revealed that there was no degradation of either bond coat or bond coat/top coat interface up to 200 hours of isothermal exposure .Interface cracking and spallation was observed after 400 hours of isothermal exposure owing to depletion of zirconia stabilizer i.e yttria and phase transformation of tetragonal zirconia to monoclinic zirconia.