Birnessite-type MnO2 nanoparticles are synthesized by mixing KMnO4 solution directly with ethylene glycol under ambient conditions. When cobalt exists in the solution, the micro-morphology of the products transforms from conglomeration to dispersive state. The result of transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) shows that the product is constructed with nanosphere in sizes of ca. 40 nm. These nanospheres are twisted by nanorods clusters. X-ray diffraction (XRD) pattern shows that the products are birnessite-type. The electrochemical properties of the prepared materials are studied using cyclic voltammetry (CV) and galvanostatic charge-discharge test in aqueous electrolyte. The product shows a very high specific capacity of 326.4 F g(-1). These results indicate that cobalt has great effects on the micro-morphology and electrochemical properties of manganese dioxide. (C) 2012 Elsevier B.V. All rights reserved.