The coupling between iron (Fe) and carbon (C) and the activity of Fe reducing bacteria (FeRB) can strongly affect C sequestration in paddy soils. Although the geochemical cycling of C and Fe has been reported at individual sites, a lack of information exists across soil types and regions. In this study, we investigated the coupling of Fe-C and the role of FeRB across five contrasting paddy soils, which account for 60 % of China’s rice cultivation area. The high iron oxides and low iron-reducing bacteria in Cumulic Anthrosols and Eutric Cambisols is conducive to soil organic carbon sequestration. The high molar ratio of carbon to iron in Eutric Cambisols can form Fe-OM through complexation. The existence of the iron and carbon relationship in Cumulic Anthrosols and Eutric Cambisols also revealed the inhibitory effect of low quantities of Fe(II) on phenol oxidase enzyme activity and SOC release. However, the high Fe(II) contents and iron-reducing bacteria, and low iron oxides in Haplic Solonchaks, Calcaric Fluvisols promote iron reduction and carbon release. Our study highlights the importance of soil characteristics on Fe-C coupling in the biogeochemical cycle through interactions among Fe morphology and microorganisms via different oxidation–reduction conditions.