A novel monomer, 2,6-di(thiophene-2-yl)-3,5bis(4-(thiophene-2-yl)phenyl)dithieno[3,2-b;2',3'-d]thiophene (Th4DTT) has been synthesized and used as an electro-active material. It has been electropolymerized onto glassy carbon (GC) electrode in sodium dodecyl sulfate (SDS) solution (0.1 M) together with multi-walled carbon nanotubes (MWCNT). A good capacitive characteristics for P(Th4DTT)/MWCNT composite has been obtained by electrochemical impedance spectroscopy (EIS), which is, to our best knowledge, the first report on capacitor behavior of a dithienothiophene. A synergistic effect has been resolved by Nyquist, Bode-magnitudephase and admittance plots. Specific capacitance of the conducting polymer/MWCNT, calculated from cyclic voltammogram (CV) together with area and charge formulas, has been found to be 20.17 F g(-1). Long-term stability of the capacitor has also been tested by CV, and the results indicated that, after 500 cycles, the specific capacitance is 87.37% of the initial capacitance. An equivalent circuit model of R-s(C-1(R-1(Q(R2W))))(C2R3) has been obtained to fit the experimental and theoretical data. The double layer capacitance (C-dl) value of P(Th4DTT)/MWCNT (4.43 mF cm(-2)) has been found to be 25 times higher than P(Th4DTT) (C-dl= 0.18 mF cm(-2)). (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40061.