Fe-based metal oxide nanomaterials have attracted significant attention as the electroanalytical sensing for heavy metal ions (HMIs) detection. It is recently found that their activities should be mainly ascribed to their valance change behavior (i.e. the Fe²⁺/Fe³⁺ cycle). However, how to promote the Fe²⁺/Fe³⁺ cycle to further increase their detection performance is highly desired yet challenging. Herein, the nanocomposite of Fe₃O₄/MoS₂ is developed as a sensing for the electrochemical detection of the highly toxic As(III). Through a series of characterizations including the XPS and DFT, the Fe₃O₄/MoS₂ shows an accelerated electron transfer induced by the valence change of Fe²⁺/Fe³⁺ cycle. The active Mo⁴⁺ on MoS₂ can serve as electron doner to reduce the Fe³⁺ to Fe²⁺ on Fe₃O₄, and thus promotes the Fe²⁺/Fe³⁺ cycle. Moreover, the synergistic effect between the excellent adsorption ability of Fe₃O₄ towards As(III) and the good conductivity of MoS₂ will further benefit to the detection. As expected, the Fe₃O₄/MoS₂ reflects an outstanding detection performance to As(III) with a sensitivity of 4.16 μA•ppb^–1, which even much outperforms than that of noble-metal materials. Overall, these discoveries are expected to drive great advances in the application of the accelerated valence change behavior for electroanalysis.