Nanoporous activated carbons (AC) has been prepared from low-cost agro-waste corncob powder by phosphoric acid-activation and investigated their electrochemical supercapacitor and sensing properties. Surface areas and pore volumes are found in the range of 690 - 1288 m2 g-1 and 0.49 - 1.64 cm3 g-1, respectively and could be controlled by adjusting the weight ratio of corncob and phosphorous. The corncob-derived AC showed excellent electrochemical performance giving a maximum specific capacitance ca. 340.8 F g-1 at scan rate of 5 mV s-1. At relatively high scan rate of 100 mV s-1 the specific capacitance of 133.7 F g-1 was obtained. About 96% capacitance retention rate was achieved even after 1000 cycles demonstrating potential usages of the materials in high performance supercapacitor electrodes. Furthermore, our AC showed excellent solvent vapor sensing performance with high selectivity for ammonia molecule.