A novel and scalable synthesis approach to produce hierarchically aligned porous carbon nanotube arrays (PCNTAs) on flexible carbon fibers (CFs) is developed. The PCNTAs are obtained by catalytic conversion of ethanol on ZnO nanorod arrays and then reduction-evaporation of ZnO nanorods, resulting in uniform and controllable wall thicknesses of the final PCNTAs. The 3D arrangement, the diameters, and the lengths of the PCNTAs can be tuned by adjusting the synthesis protocols of the ZnO nanorod arrays. The PCNTAs@CFs exhibit a high specific capacitance of 182 F g(-1) at 40 A g(-1) (188 F g(-1) at 20 A g(-1)) in 6 M KOH. The symmetric supercapacitor shows an excellent cycling stability with only 0.0016% loss per cycle after 10 000 continuous cycles at the current density of 12 A g(-1). These excellent electrochemical performances are ascribed to the unique structural design of hierarchical PCNTAs, which provide not only appropriate channels for enhanced electronic and ionic transport but also increased surface area for accessing more electrolyte ions. The structural design and the synthesis approach are general and can be extended to synthesizing a broad range of materials systems.