MnO2 hierarchical microsphere has been synthesized by a facile and direct hydrothermal reaction between KMnO4 and HCl without the aids of catalysts, surfactants or templates. The as-prepared microsphere, as characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis and nitrogen adsorption and desorption, is in form of K0.27MnO2 (H2O )0.54, with a flower-like hierarchical microsphere structure and a BET surface area value of 52 m2/g. The morphology of the product can be simply tailed by controlled by reaction temperature or period and crystallinity can be modified by changing the concentrate of KMnO4. In general, excessive KMnO4 and low hydrothermal temperature are favor to forming flower-like hierarchical structure. Besides, the formation mechanisms of the hierarchical schemes are proposed.