Abstract: The characteristics of rust layer on steel immersed in seawater and related anaerobic microbial community were investigated. Sulfate-reducing bacteria and iron-reducing bacteria were found in the rust layer by microbial enrichment and molecular biological analysis. The characteristics of rust layer minerals were studied and analyzed by SEM, XRD and EDS. In the outer and middle rust layers, the iron oxides（ including α, β, γ-FeOOH） were found, and the green rust was mainly found in the inner rust layer. The formation and transformation of rust layer minerals under the influence of anaerobic bacteria was discussed on the basis of experimental observation. It is also suggested that microorganisms and related rust layer minerals on steel possibly play an important role in marine microbial remediation.