Polyaniline/graphene (PANI/graphene) composites are the most investigated electrode materials for supercapacitors, owing to their high specific capacitance and excellent rate performance. However, a specific capacitance larger than the theoretical limit of the composite has been frequently reported for PANI/graphene composites, and the reason for this over-high capacitance has not been understood. In this work, after systematically investigating the evolution of the electrochemical and spectral properties of PANI/graphene, we prove that the hydroxyl- or amino-terminated oligoanilines generated from degradation of PANI possess a large specific capacitance (>1000 F g⁻¹), and they significantly increase the total specific capacitance of the composite electrode. Graphene in the composite serves as a conductive matrix for electron transport between the low-conductivity hydroxyl or amino-terminated oligoanilines and the current collector. Based on the above results, we put forward a suggestion for simultaneously improving the specific capacitance and cycling stability of the PANI/graphene composites. A PANI/reduced graphene oxide composite material with a specific capacitance of 719 F g⁻¹ at 1.4 A g⁻¹ and 91.3% capacitance retention after 10 000 cycles is obtained.