 Nanocomposites consisting of zeolitic imidazolate framework nanocrystals on graphene oxide (ZIF/GO) are prepared by a facile ultrasonic method under ambient conditions. Brunauer–Emmett–Teller specific surface area measurements show that surface areas of the graphene composites are greatly increased by the addition of the ZIF component. Electrochemical properties of the nanocrystal-modified electrodes are measured by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy in 6 M KOH electrolyte. Nanocomposites of ZIF-8/GO and ZIF-67/GO exhibit high specific capacitance values up to 400 and 252 F g−1, respectively, much higher than that of each ZIF by itself. In addition to the good pseudocapacitive behavior, they exhibit excellent cycling performance, indicating that the ZIF nanoparticles grown on the surface of GO are beneficial to improving electrochemical properties.