<P><B>Abstract</B></P> <P>In natural and engineered anaerobic ecosystems, syntrophic oxidation of short-chain fatty acid is one of the key factors and interspecies electron transfer mechanisms between bacteria and archaea play a pivotal role. Growing evidence suggests that microorganisms have the capability to promote interspecies electrons transfer in a more direct manner. In the current study, three different types of iron oxides were used to thermophilic anaerobic reactors (at 50 °C), quantitative polymerase chain reaction and 16S rRNA sequencing technique were applied to investigate the relation between iron reduction bacteria and syntrophic acetate oxidation bacteria. Experiment results showed that goethite and hematite promoted the methane production and generation rate and partially relieved the negative effects of H<SUB>2</SUB>. The syntrophic relation between <I>Syntrophaceticus</I> and <I>Methanobacterium</I> worked with a direct interspecies electron transfer model rather than interspecies hydrogen transfer in goethite and hematite dosed reactors. The gene copies of <I>Syntrophaceticus</I> predominated over that of <I>Geobacter</I>. Theoretical calculations revealed that the rates of iron oxide mediated interspecies electron transfer among syntrophic partners were 10<SUP>5</SUP>-10<SUP>6</SUP> times higher than those attainable via interspecies H<SUB>2</SUB> transfer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Iron oxide promoted the growth of <I>Syntrophaceticu</I>s rather than <I>Geobacter</I>. </LI> <LI> DIET happened between acetate oxidation bacteria and methanogenic archaea. </LI> <LI> Theoretical iron oxides-mediated electron transfer rate was higher than H<SUB>2</SUB>. </LI> <LI> Maximum electron carrier flux was 9.0 × 10<SUP>−6</SUP> A in goethite reactor. </LI> </UL> </P>