Abstract <p>Porous Zn–Fe₂O₃ nanozymes were prepared through calcination of a Zn-MIL-53 precursor via a MOF-to-oxide conversion strategy. Benefiting from the self-sacrificial template effect and Zn incorporation, the obtained Zn–Fe₂O₃ retained the spindle-like morphology while developing a hierarchical micro/mesoporous structure with a larger specific surface area than Fe₂O₃. Meanwhile, Zn incorporation increased the Fe²⁺/Fe³⁺ ratio and enriched oxygen vacancy related defects, which collectively facilitated H₂O₂ activation and enhanced the peroxidase-like (POD-like) catalytic oxidation of TMB. As a result, Zn–Fe₂O₃ exhibited significantly higher POD-like activity than Fe₂O₃. Based on this enhanced catalytic performance, an inhibition-type colorimetric assay for acetylcholinesterase was established using acetylthiocholine as the substrate. Under the optimized conditions, the assay showed a linear range of 0–35 mU/mL and a detection limit of 0.144 mU/mL. This work demonstrates that combining MOF-derived porosity with dopant-induced electronic and defect modulation is an effective strategy for developing Fe-based nanozymes for nanozyme-based colorimetric AChE activity assays.</p>