Phosphate-functionalized carbon nanotube (CNT)-containing carbon composites with hierarchical porous structure have been synthesized by a simple soft-template hydrothermal method followed by heat treatment. The resulting carbon composites are characterized by FE-SEM, TEM, TGA, FTIR microspectroscopy, and nitrogen sorption techniques. The electrochemical performance of the carbon composites as electrode materials for supercapacitors is also investigated. The results show that CNTs can be uniformly embedded in the carbon matrix, and the phosphate groups are introduced into the carbon composites successfully. The addition of CNTs with suitable content significantly improves the rate capability of carbon composites in 6 M KOH aqueous solution. Cell voltage window can be extended to 1.2 V when increasing the heat treatment temperature of carbon composites to 800 °C, and the resulting composites exhibit highly stable performance in supercapacitors at high current load of 5 A g(-1) and wide cell voltage of 1.2 V.