Copper has long been utilized as a disinfectant for bacteria, but its impact on microbial communities attached to the steel surface in seawater remains unknown. In the present study, 3 mooring chain steels of different copper contents are subjected to a 3-month marine field exposure, and the corrosion rate increases in the order of BR5 steel (without copper) < BR5CuH steel (0.8％ copper) < BR5CuL steel (0.4％ copper). The microbial community results show that copper introduction does not result in an obvious change in microbial quantity, but it alters the diversity, richness, and structure of microbial communities due to the variation in copper-resistance of different species. BR5CuH steel holds microbial communities with the highest percentage of some well-known corrosive microbes including sulfate-reducing bacteria, sulfur-oxidizing bacteria, and iron-oxidizing bacteria, but possesses the lowest community diversity/richness owing to the toxicity of copper. The microbial community diversity/richness is stimulated by the low-copper content of BR5CuL steel, and this steel also carries an intermediate proportion of such corrosive bacteria. Both well-known corrosive bacteria and microbial community diversity/richness seem to be involved in the corrosion acceleration of copper-bearing mooring chain steels.