An ideal carbon-based supercapacitor electrode requires abundant micropores that are favorable for charge accumulation, and suitable mesopores that are beneficial for fast electrolyte ions transport. Herein, 3D porous carbon microspheres (carbon nanotube-ketjen black/activated carbon, CNT-KB/AC), where the CNT-KB microspheres (CKMS) as the framework providing mesopores and the activated carbon as the core providing micropores, have been constructed by spray drying and KOH activation. The obtained carbon composites exhibit a homogeneous spherical structure and high specific surface area (up to 1751 m(2) g(-1)). The CNT-KB/AC electrode with an areal density of 3 mg cm(-2) can achieve a high areal capacitance of 506.9 mF cm(-2) at the current density of 0.2 A g(-1) in 6 M KOH solution, which is much larger than that of the CNT/AC electrode (232.6 mF cm(-2)) and CNT-AB/AC electrode (179.5 mF cm(-2)). Besides, when the areal density is increased up to 9 mg cm(-2), the areal capacitance of CNT-KB/AC is increased up to 998.9 mF cm(-2) at 0.2 A g(-1) and 724.9 mF cm(-2) at 20 Ag-1. Furthermore, it exhibits excellent long-term cycling stability (achieving capacitance retention of 94% after 10,000 cycles). These results indicate that the CNT-KB/AC composites are promising electrode materials for high-areal-density supercapacitors.