How to prepare porous carbons with appropriate structure for supercapacitors is a big challenge. In general, activation is the simplest way to obtain porous carbons. Porous bamboo-like CNTs were fabricated by simple activating sulfonated polymer nanotubes with steam at 800 degrees C. Compared with the un-activated one, activated carbon nanotubes (ACNTs) have good tubular structure, larger specific surface area and rich porosity thanks to the protection of steam during the activation. The ACNTs electrode for supercapacitors displays a specific capacity of 276 F g(-1)at 1 A g(-1). When assembling ACNTs into a symmetrical supercapacitor, the specific capacity of the device can retain 98% after 10 000 cycles, and this result shows the great application prospect of ACNTs for supercapacitors.