Enhanced oxygen vacancy (V_O) has been designated as an effective strategy to prepare high-performance MnO₂ nanocatalysts for the oxidation of volatile organic compounds (VOC) for thereof unbalanced electronic structure, and rapid electron transfer which may even reduce the reaction temperature down to room temperature. Herein, the effects of the V_O on the catalytic performance of nano-sized MnO₂ were discussed by classifying the V_O into surface-anchored and bulk-involved ones. Currently used introducing and modulating methods for V_O including elemental doping, energetic particle bombardment, atmosphere heat treatment, mechanical chemistry, and redox methods are detailly reviewed. Corresponding regulating mechanisms for V_O are expounded. Commonly used characterization methods including ESR, XPS, HRTEM, and UV-vis are reviewed. Furtherly, the unveiled question which is highly expected to be answered on V_O of MnO₂ nanocatalysts is proposed. The purpose of this review is to present the current status of research on MnO₂ nanoparticles and to provide researchers with basic research ideas.