The power units in modem electric vehicles are required to store large amount of energy and to provide a high power. Supercapacitors being able to export a pulsed high power can be used in combination with batteries or fuel cell to meet the energy and power demand of electric vehicles. Carbon nanotubes with high surface area and conducting polymers with large pseudocapacitance are both powerful candidates for supercapacitors. This thesis describes a novel electrochemical route for synthesis of composites of conducting polymer and nanotubes via co-deposition from solutions containing ionic CNTs and monomers. The resulting deposits exhibited a unique porous network structure composed of individual nanotubes coated with a layer of conducting polymers. Carbon nanotubes served as charge carriers during the polymerisation and also acted as both a strong backbone and effective dopant within the composite materials. Therefore, the composites have improved mechanical integrity and an open structure that facilitates ion and solvent motion during the electrochemical processes. Moreover, the large immobile CNT anions exert an electrostatic repulsion to the electrons on the polymer chain. This repulsion makes it easier to remove electrons from the polymer chains. As a result, the composites showed good conductivity and capacitive properties even at negative potentials. A systematic study on the charge storage properties of the composites has been carried out using various electrochemical methods, including CV, AC impedance spectroscopy, chronocoulometry, chronoamperometry and chronopotentiometry. FTIR and XPS have been used to study the interaction between CNTs and conducting polymers. Prototype supercapacitors were built with the composites as electrode material. Both symmetric and asymmetric prototypes showed ideal capacitive behaviour, indicating a good potential for application in supercapacitors using the novel composite materials.