Novel ultramicroporous carbon nanoparticles (UCNs) are synthesized on the basis of solvothermal polymerization of phloroglucinol and terephthaldehyde in dioxane at 220 degrees C, followed by carbonization at 850 degrees C. The resultant UCNs show regular 0.54 nm ultramicropores and particle sizes of similar to 30 nm. The UCNs as electrode materials for electrical double-layer capacitors (EDLCs) show a specific capacitance of 206 F g(-1) at 1.0 A g(-1) in a 6 M KOH aqueous solution. The UCN electrode is suitable for charge discharge operation even at a very high current density of 50 A g(-1) coupled with a capacitance of 135 F g(-1), indicating excellent high-rate electrochemical performance. The electrochemical capacitance of the UCN electrode has a high retention of 97.6% after 5000 cycles at 1.0 A g(-1) tested by a standard three-electrode system (97.3% for the two-electrode cell), which implies a good electrochemical cycling life. This study highlights promising prospects of novel UCNs as advanced electrode materials for EDLCs where a high level of current charge and discharge is required.