The detonation nanodiamond is a versatile-low-cost nanomaterial with tunable properties and surface chemistry. In this work, it is shown how application of nanodiamond (ND) can greatly increase the performance of electrochemically active polymers, such as polyaniline (PANI). Symmetric supercapacitors containing PANI-ND nanocomposite electrodes with 3-28 wt% ND show dramatically improved cycle stability and higher capacitance retention at fast sweep rate than pure PANI electrodes. Contrary to other PAN I-carbon nanocomposites, specific capacitance of the selected PANI electrodes with embedded ND increases after 10 000 galvanostaticycles and reaches 640 F g(-1) when measured in a symmetric two electrode configuration with 1 M H2SO4 electrolyte. The demonstrated sepecifc capacitance is 3-4 times higher than that of the activated carbons and more than 15 times higher than that of ND and onion-like carbon (OLC).