A major challenge in the synthesis of porous metal oxides is the control of pore size and/or wall thickness that may affect the performance of these materials. Herein, nanoporous β-MnO2 samples were prepared using different hard templates, e.g., ordered mesoporous silica SBA-15 and KIT-6, disordered mesoporous silica, and colloidal silica. These samples were characterized by Powder X-Ray Diffraction (PXRD), Transmission Electron Microscopy (TEM), and N2 adsorption-desorption. The pore size distribution of β-MnO2 was tuned by the different hard templates and their preparation details. Catalytic activities in CO oxidation and N2O decomposition were tested and the mesoporous β-MnO2 samples demonstrated superior catalytic activities compared with their bulk counterpart.