Sulfamic acid (SFA)-doped poly(3,4-ethylenedioxythiophene) (PEdot) grown on expanded graphite (EG) nanohybrids (S-PEdot/EG) were synthesized by surfactant-free in situ chemical oxidative polymerization. The 3D hierarchical structure S-PEdot/EG with homogenous ridgelike surface morphology was achieved by intercalating 3,4-ethylenedioxythiophene monomers between the interlayers of EG using a vacuum-assisted method. The composition of the nanohybrids and the π-π interaction between the EG and PEdot molecules were characterized by using Raman spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The nanohybrid with an EG content of 10%exhibited excellent capacitive performance with a high capacitance of 139.6 Fg^sup -1^ at 1.0 Ag^sup -1^ in 1 m LiClO^sub 4^ electrolyte. In the two-electrode symmetric supercapacitors, the device performed with a high energy density of 6.83 Whkg^sup -1^ at the power density of 146 Wkg^sup -1^, and retained high stability during the charge-discharge process. The excellent performance can be attributed to the 3D hierarchical structure, the π-π interaction between EG and PEdot molecules, andthe doped SFA as an immobilized counter-ion. This cost-effective and simple methodused to fabricate 3D S-PEdot/EG nanohybrids is promising for the generation of electrode materials for high-performance supercapacitors.