Mesoporous manganese oxide (MPMO) K_0.216MnO₂ 1.26H₂O was synthesized by reduction of KMnO₄ with maleic acid. Its composition and structure were analyzed and characterized by inductive coupled plasma atomic emission spectrometry (ICP-AES), titration, X-ray powder diffractometry (XRD), thermogravimetry (TG)-differential thermoanalysis (DTA). The morphology and pore structure of the MPMO material were accomplished by means of high-resolution transmission electron microscopy (HRTEM) and N₂ sorptometry and transmission electron microscopy (TEM). The results show that MPMO is a pseudocrystalline material with complex network pore structure; its BET surface area is 261.6 m²/g and pore diameter distribution is approximately in the range of 2–10 nm. The MPMO material turns into -MnO₂ when the calcinating temperature rises to 400°C.