Porous Mn3O4 nanoparticles with tunable microstructures are synthesized from Mn(AcO)2·4H2O with Pluronic F127 as a dispersant. The amount of copolymer served as the surfactant in the precursor solution is varied to change/tune the specific surface area/porosity of Mn3O4. The textural and electrochemical properties of porous Mn3O4 nanoparticle are systematically characterized by means of the N2 adsorption/desorption isotherms, scanning electron microscopic (SEM), transmission electron microscopic (TEM), X-ray diffraction (XRD), and voltammetric analyses. The interactions between manganese precursor and triblock copolymer can be used to control the microstructures of resultant oxides. Mn3O4 nanoparticles with tunable porosity and high surface area achieve the excellent capacitive performances (e.g., high-power characteristics and impressive capacitance retention) for next generation supercapacitors. The specific surface area indicating the electrochemically active sites for charge storage/delivery as well as the pore structure indexed by the BJH pore volume, which affects the ion transportation and electrolyte permeation, have been demonstrated to be the key factors determining the capacitive performances of Mn3O4 in the low-rate and high-rate processes, respectively.