Activated carbons for supercapacitor electrodes are prepared from sugar cane bagasse using chemical activation with ZnCl2. The ZnCl2 activation of bagasse is studied using thermogravimetric analysis and the carbon pore structures are characterised using N2 and CO2 adsorption. In two-electrode, sandwich-type supercapacitor cells containing 1M H2SO4 the sugar cane bagasse carbons (SCCs) exhibit specific energy up to 10Whkg−1 and specific capacitance close to 300Fg−1. The electrochemical performance of the SCCs is attributed to their high specific surface area and the development of mesopores with ZnCl2 impregnation ratios of 1 or greater. By contrast, the pyrolysis of bagasse without ZnCl2 produces a carbon with low specific capacitance. The SCC prepared with a ZnCl2 ratio of 3.5 shows the most stable electrochemical performance at fast charge–discharge rates.