To reduce the size of Ni(OH)(2) aggregates is an effective way to improve their capacitive performance for the electrodes of supercapacitors. The ultrasmall Ni(OH)(2) aggregates (1-2 nm) on active carbon (AC) can be obtained by depositing the soluble precursor of Ni(OH)(2) on AC at low temperature. The Ni(OH)(2)/AC samples were characterized by SEM, TEM, XRD and XPS. The specific capacitance of ultrasmall Ni(OH)(2) aggregates in the Ni(OH)2/AC composite can reach 2949 F g(-1) at a scan rate of 20 mV s(-1), which is higher than its theoretical specific capacitance (2382 F g(-1)). Ni(OH)(2) aggregates supported on carbon cloth can also exhibit superior specific capacitance as a bind-free flexible electrode. The capacitive, rate and cycling performance of ultrasmall Ni(OH)(2) aggregates on AC are excellent, revealing the great potential of ultra small sized materials in energy storage. (C) 2016 Elsevier Inc. All rights reserved.