Mesoporous activated carbons (ACs) were successfully prepared from lignite using KOH as activation agent at the temperature above 700 degrees C. The pore structure and surface chemistry of the as-prepared ACs were characterized by means of nitrogen adsorption-desorption, X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The results show that such prepared mesoporous ACs have a high specific surface area (similar to 3036 m(2).g(-1)) with a hierarchical macro-meso-micro-pore structure and oxygen-enriched surface. The electrochemical performances of the ACs as electrode materials for electrochemical capacitors (ECs) were assessed by galvanostatic charge-discharge, cyclic voltammetry and cycling durability tests. It was demonstrated that the mesoporous ACs produced in this study possessed a maximum specific capacitance of 355 F. g(-1) and 196 F. g(-1) in 3M KOH aqueous and 1 M (C2H5)(4)NBF4/PC organic electrolytes, respectively, at a current density of 50 mA.g(-1), and exhibited a desirable energy and power density with a superior cycling performance. The excellent capacitive behavior of the prepared mesoporous ACs in aqueous system is attributed to their unique macro-meso-micro-hierarchical pore structure with high surface area and oxygen-containing surface. Their superb electrochemical performance in the organic electrolyte is attributed to their well-developed mesoporous structure. (C) 2015 Elsevier B.V. All rights reserved.