Supercapacitor electrodes fabricated from multiwalled carbon nanotubes (MWCNTs) and poly-3,4-ethlyenedioxythiophene–polystyrenesulfonate (PEDOT–PSS) with different mass ratios (MWCNTs:PEDOT–PSS=95:5, 90:10, 70:30, 50:50) were examined and compared with the electrode composed of MWCNTs and polytetrafluoroethylene (PTFE). The cyclic voltammetry (CV) results show that the MWCNTs/5wt% PEDOT–PSS composite owns the highest specific capacitance, while the MWCNTs/50wt% PEDOT–PSS composite can maintain the best capacitive behavior at higher scan rates and frequencies from the CV and EIS (electrochemical impedance spectroscopy) data. The EIS and CV results show the loss of electroactive species in PEDOT–PSS during continuous cycling. The transmission electron microscopy shows that the MWCNTs are partly covered with the polymers. The results of time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectrometry reveal that the conjugation path in the backbone of PEDOT is damaged, leading to the decline of the redox peaks in CV for the MWCNTs/PEDOT–PSS composites during continuous cycling. Whereas, the –SO3 − groups in PSS retains integrity during continuous cycling, and they can still contribute to the capacitance of the composite; therefore, when compared with the MWCNTs/10wt% PTFE composite, the MWCNTs/10wt% PEDOT–PSS composite can remain higher specific capacitance, and maintain the capacitive characteristics at higher scan rates.