We have studied the electronic states origin of the electrochemical capacitance of nanostructures by ab initio calculations. We have chosen to investigate linear carbon chains and fullerenes encapsulating several types of carbon cluster. Linear carbon chains show an oscillatory behavior of the self-capacitances depending on whether the number of atoms is even or odd. The self-capacitances of fullerenes significantly change depending on the clusters inserted into the fullerene. The essential cause for these variations of self-capacitances is due to the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and the electron density distribution of the HOMO level. (C) 2004 Elsevier B.V. All rights reserved.