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Defective MIL-88B(Fe) nanorods are exploited as exemplary iron-bearing metal−organic framework (MOF) catalyst for molecular oxygen (O 2 ) activation at ambient temperature, triggering effective catalytic oxidation of formaldehyde (HCHO), one of the major indoor air pollutants. Defective MIL-88B(Fe) nanorods, growing along the [001] direction, expose abundant coordinatively unsaturated Fe-sites (Fe-CUSs) along extended hexagonal channels with a diameter of ca. 5 Å, larger enough for the diffusion of O 2 (3.46 Å) and HCHO (2.7 Å). The Lewis acid− base interaction between Fe-CUSs and accessible HCHO accelerates the Fe III /Fe II cycle, catalyzing Fenton-like O 2 activation to produce reactive oxidative species (ROSs), including superoxide radicals (•O 2 − ), hydroxyl radicals (•OH), and singlet oxygen ( 1 O 2 ). Consequently, adsorbed HCHO can be oxidized into CO 2 with a considerable mineralization efficiency (over 80%) and exceptional recyclability (4 runs, 48 h). Dioxymethylene (CH 2 OO), formate (HCOO − ) species, and formyl radicals (•CHO) are recorded as the main reaction intermediates during HCHO oxidation. HCHO, H 2 O, and O 2 are captured and activated by abundant Fe III /Fe II -CUSs as acid/base and redox sites, triggering synergetic ROS generation and HCHO oxidation, involving cooperative acid−base and redox catalysis processes. This study will bring new insights into exploiting novel MOF catalysts for efficient O 2 activation and reliable indoor air purification at ambient temperature.