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Ferrihydrite (Fh) mineral associated soil organic matter (SOM) is considered to be protected. But the multiplicity of interactions between Fh and OM suggest OM protection can be disrupted. Under anoxic conditions, Fe(II)(aq) can transform Fh into more stabilized iron minerals and that can impact the bioavailability of associate OM under oxic conditions. To investigate this, Fe(II) reacted synthesized Fh- labeled OM coprecipitates were characterized using MBS and STEM and microbial incubation study under oxic conditions was conducted. Fe(II) reacted coprecipitates protected more coprecipitated C when the C/Fe ratio of the coprecipitates was low. This effect was related to the crystallinity changes of the coprecipitates during Fe(II) reaction. OM bioavailability in naturally occurring bacteriogenic Fe-OM coprecipitates was also measured and found the native OM was more protected than the OM in the synthesized coprecipitates. These findings will help to understand the C stabilization potential of soil under redox dynamics conditions.