Starch or starch mixed with phosphoric acid, guanidine carbonate, or guanidine phosphate is heat-treated for use as an electrode in an electrochemical capacitor. In the case of starch, the capacitance value is low (31.2 F g(-1) at 50 mA g(-1)). However, the capacitance value significantly increases with the addition of guanidine phosphate, which can act as a flame-retardant (124.1 F g(-1) at 50 mA g(-1)). The method used in this study, which involves mixing with a flame-retardant by immersion, should be a promising candidate for improving of the capacitance value of starch-derived carbon. (C) 2011 Elsevier B.V. All rights reserved.