The interaction of naturally occurring minerals with H2O2 affects the remediation efficiency of polluted sites in in situ chemical oxidation (ISCO) treatments. However, interactions between vanadium(V) minerals and H2O2 have rarely been explored. In this study, H2O2 decomposition by various vanadium-containing minerals including V(III), V(IV), and V(V) oxides was examined, and the mechanism of hydroxyl radical (•OH) generation for contaminant degradation was studied. Vanadium minerals were found to catalyze H2O2 decomposition efficiently to produce •OH for diethyl phthalate (DEP) degradation in both aqueous solutions with a wide pH range and in soil slurry. Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analyses, and free radical quenching studies suggested that •OH was produced via single electron transfer from V(III)/V(IV) to H2O2 followed a Fenton-like pathway on the surface of V2O3 and VO2 particles, whereas the oxygen vacancy (OV) was mainly responsible for •OH formation on the surface of V2O5 particles. This study provides new insight into the mechanism of interactions between vanadium minerals and H2O2 during H2O2-based ISCO.