Abstract Polyaniline (PANI) is a promising electrode material for supercapacitors, but its reported specific capacitance is much lower than its theoretical capacitance. This is because the PANI molecular chains are tightly packed, and the electrolyte is left with a difficult path to penetrate into the interior regions of PANI. Large anions can be doped into PANI and expand the distance between adjacent PANI molecular chains, thereby increasing the utilization of PANI. In this work, Nafion‐doped PANI was synthesized by in situ chemical polymerization in aniline monomer and Nafion solution and the Nafion content was tuned to improve the overall performance. The specific capacitance of Nafion‐doped PANI with an optimized Nafion content (4.76 wt %) reached 603.9 and 378.4 F/g at 1 and 50 mV/s), which are both higher than that of PANI (580.0 and 347.7 F/g at 1 and 50 mV/s). The capacitance retention of Nafion (16.67 wt %)‐doped PANI was 64.89 % after 1000 cycles, which is better than that of PANI alone (20.25 %). This work provides a facile approach to increasing the utilization of PANI as an electrode material for supercapacitors.