Abstract: The influence of sensitisation treatment on the intergranular corrosion properties of 825 alloy is investigated by 50 % sulphuric acid-iron sulphate intergranular corrosion test and polarisation curve analysis, and the causes are observed and analysed by metallography (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the corrosion rate and corrosion current density of the sensitized specimen of 825 alloy held at 750 ℃ for 1 h are 57 % and 48 % of those of the solid solution specimen, respectively. There are no precipitate precipitation at the grain boundaries of the sensitized and solid solution specimens, and no chromium-poor zones around the grain boundary, therefore, the material has no intergranular corrosion susceptibility. However, there are differences in potentials between the precipitated TiN and Ti(C,N) particles within the grains and the substrate, which can easily lead to the occurrence of pitting corrosion. After sensitisation treatment at 750 ℃ for 1 h, the grain size of the 825 alloy is uniform, the distribution of TiN and Ti(C,N) particles precipitated is uniform, and the corrosion resistance of the material is enchanced.