<p>MgFe₂O₄ spinel ferrites have attracted increasing interest as magnetically recyclable photocatalysts owing to their narrow bandgap (~ 1.9&#xa0;eV) and structural robustness; however, their photocatalytic efficiency is often limited by rapid charge‐carrier recombination. In this work, Mg_1-xZn_xFe₂O₄ (x = 0–0.15) photocatalysts were synthesized via co-precipitation route, and the combined effects of Zn²⁺ doping and calcination temperature (700–900℃) on their structural, optical, and photocatalytic properties were systematically investigated using a full factorial experimental design. XRD and TEM analyses confirm the successful incorporation of Zn²⁺ into the spinel lattice without secondary phase formation, accompanied by enhanced crystallinity at elevated calcination temperatures. UV–Vis diffuse reflectance spectra reveal a modest enhancement of visible-light absorption (600–800&#xa0;nm) with increasing Zn²⁺ content, while the fundamental bandgap slightly widens from 1.88&#xa0;eV (undoped) to 1.95–1.98&#xa0;eV upon Zn²⁺ substitution. Photocatalytic degradation of methylene blue under UV irradiation demonstrates a distinct global performance maximum at x = 0.10 and 800&#xa0;°C, yielding a degradation efficiency of 97.23% and an apparent rate constant of 0.0402&#xa0;min⁻¹, which is ~ 1.56 times higher than that of undoped MgFe₂O₄ under identical conditions. Radical scavenging experiments indicate that hydroxyl radicals are the dominant reactive species, predominantly generated via electron-mediated oxygen reduction pathways. The observed enhancement arises from a non-additive, synergistic interaction between Zn²⁺-induced electronic modulation and temperature-controlled crystallinity, rather than from surface area or bandgap narrowing alone. This study provides quantitative evidence for synergistic optimization in doped spinel ferrites and offers guidance for the rational design of efficient, recyclable magnetic photocatalysts.</p>