A flexible composite electrode, which is composed of conducting polyaniline (PANI) as electroactive material and flexible graphite (FG) as conducting substrate, has been fabricated by in situ chemical polymerization to substitute for the expensive Pt counter electrode (CE) used in dye-sensitized solar cells (DSCs). The photovoltaic parameters of DSCs are strongly dependent on the oxidation state and the thickness of the PANI film. Higher photocurrent density and efficiency have been obtained by using emeraldine PANI compared to pernigraniline. The fabrication conditions, such as reaction time and initial monomer concentration, have been investigated to control the thickness of the PANI film. With initial monomer concentration of 0.3 M and reaction time of 60 min, an optimized PANI/FG composite CE with a PANI film thickness of 330 nm has been obtained. A DSC with the composite CE shows an overall conversion efficiency of 7.36%, which is comparable to 7.45% of that with Pt electrode under the same test condition. Facile charge-transfer and low sheet resistance of the composite electrode are suggested to be responsible for high performance of the DSC using such CE.