The effect of thermoacidophilic archaeon Metallosphaera cuprina (M.cuprina) on the corrosion of Q235 carbon steel in its culture medium was investigated in this work.In the sterile culture medium,the carbon steels showed uniform corrosion morphologies and almost no corrosion products covered the sample surface during 14 days of immersion test.In the pres-ence of M.cuprina,some corrosion pits appeared on the surface of carbon steels in the immersion test,exhibiting typical localized corrosion morphologies.Moreover,the sample surfaces were covered by a large number of insoluble precipitates during the immersion.After 14 days,the thickness of precipitates reached approximately 50 μm.The results of weight loss test and electrochemical test demonstrated that the carbon steels in the M.cuprina-inoculated culture medium had higher corrosion rate than that in the sterile culture medium.The oxygen concentration cell caused by M.cuprina biofilms resulted in localized corrosion behavior,and the ferrous oxidation ability of M.cuprina accelerated the anodic dissolution of carbon steels,thus promoting the corrosion process of carbon steels.