<p>The formation mechanism of arc mafic rocks with heavy iron isotope signature remains enigmatic. Here we report Fe-Mo-Sr-Nd-Hf isotope data of arc rocks from Northeast China. The studied arc rocks have δ⁵⁶Fe values (0.08‰ to 0.23‰) comparable to or higher than those of mid-oceanic-ridge basalts, and enriched Sr-Nd-Hf isotope compositions. Combined with the published data of global arc mafic rocks, we find there is a correlation between the δ⁵⁶Fe values and radiogenic Sr-Nd isotopes, indicating that sediment recycling may have affected the iron isotope of arc rocks. Notably, the positive correlation between the δ⁵⁶Fe and δ⁹⁸Mo values further suggests that the metasomatism of mantle wedge peridotite by anoxic sediment-derived melts may be the first-order control for the heavy iron isotopes of arc mafic rocks. Therefore, the arc rocks with heavy iron isotopes can be explained by the addition of anoxic sediments to their mantle sources.</p>