We report on a strategy to enhance electrochemical capacitive properties of the graphene oxide-poly(3,4-ethylenedioxythiophene) (GO-PEDOT) composites. The basic idea is to convert GO to carboxylated GO (CGO) via carboxylation treatment. Composite electrodes of CGO-doped PEDOT (CGO-PEDOT) are fabricated by in situ electrochemical polymerization, which make adequate use of oxygenated groups on the basal plane of CGO to combine with PEDOT for enhanced supercapacitive properties. During carboxylation, hydroxyl and epoxide groups on GO are converted to carboxyl groups, as characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Electrochemical measurements show that CGO-PEDOT electrodes have boosted supercapacitive performances as compared to GO-PEDOT. In CGO nanosheets, the edges and basal planes are both covered with carboxyl groups, providing more active sites for combination with PEDOT coating, in contrast to GO nanosheets that only use edged carboxyl groups. The as-prepared CGO-PEDOT composite electrodes exhibit superior rate capability, high areal specific capacitance (90.9 mF cm(-2) at 10 mV s(-1)), and excellent cycling stability (retaining 99.6% of initial capacitance for 5000 cycles). This work is anticipated to stimulate further research interest for CGO-based composite electrodes in electrochemical energy storage.