Hierarchical three-dimensional porous carbon has been prepared through facile and moderate carbonization of Enteromorpha prolifera, a sustainable biomass-based carbon source. The novel carbonization process retains the original algae cell morphology with unusual egg-shell-like structure and develops porosity. Both the Enteromorpha prolifera derived porous carbon and its polyaniline (PANI) composites, synthesized by rapid in-situ electrochemical deposition, have been fabricated into supercapacitor electrodes. Both the electrodes exhibit distinguished and long-lasting capacitance. The porous carbon and PANI composite electrode realizes initial capacitance of 622Fg−1, 3 times that of Enteromorpha prolifera derived carbon electrode (180Fg−1), and remains 87% capacitance retention rate after 2000 charge/discharge cycles at 1Ag−1 current density. The investigation demonstrates the great potential of high-performance carbon composite materials and whose energy storage device may be derived from Enteromorpha prolifera, a biomass-based sustainable carbon source as a result of a sea waste invoking great environment concerns.