The romanechite-like sodium manganese oxide Na(2)Mn(5)O(10) is synthesized through alkaline hydrolysis of [Mn(12)O(12)(CH(3)COO)(16)(H(2)O)(4)] followed by thermal calcination. Amorphous Na(2)Mn(5)O(10) is obtained at relatively low temperature (200 degrees C). Increasing the calcination temperature leads to highly crystalline nano-rods. Electrochemical studies demonstrate that Na(2)Mn(5)O(10) is a good candidate as positive electrode materials for supercapacitor: specific capacitances of 178, 173 and 175 Fg(-1) are obtained for Na(2)Mn(5)O(10) calcined at different temperatures (200, 400 and 600 degrees C), respectively, by charge-discharge tests at 0.1 A g(-1). Moreover, capacitance losses of all the products in 1000 cycles are less than 3%. (C) 2011 Elsevier B.V. All rights reserved.