The effects of phenols on hydrochloric acid leaching of metal oxides is investigated theoretically. A mathematical model is developed for the early stages of leaching assuming that steady state conditions and Fick's first law are valid for the formation and diffusion of metal cations through the Helmholtz-Stern interface. It is found theoretically that the leaching rate is exponentially proportional to acid and phenol concentrations and any metal-phenol complex which can be decomposed by chloride ions should considerably increase the leaching rate by playing a role of active transport. Otherwise, phenols are expected to have a synergistic effect on the hydrochloric acid leaching of metal oxides. The validity of this theoretical approach is checked by examining the effect of phenol and resorcinol on HCl-CH3OH and HCl-C2H5OH leaching of ilmenite at 3 M HCl concentration. The mathematical model is verified by regression analysis of the data collected.