In this study, we used a two-stage process and phosphoric acid to thermochemically transform waste biomass rice straw into porous carbon (PC) for the preparation of high-performance supercapacitor electrodes. The morphological and chemical characteristics of PC were investigated by X-ray diffraction, scanning electron microscopy, surface area, and porosity analyses by the BET (Brunauer, Emmett, and Teller) nitrogen adsorption method, Fourier transform infrared spectroscopy. The modification process leads to the increase in the specific surface area and pore size of PC. The dc conductivity of the samples determined at room temperature was found to increase from 16.1 × 10−5 to 10.16 × 10−3 Ω−1 cm−1. The samples showed good electrochemical property with specific capacitance possessing in the range of 56–112 F/g. It was found that the carbonization temperature plays a crucial role on the evolution of structural and electrochemical properties of porous carbons. These porous carbons which show a particular large reversible capacity are proved to be promising electrode materials for high-rate and high-performance supercapacitors. © 2014, Springer Japan.