Poly(3-chlorothiophene) (PCT) films were synthesized electrochemically by direct oxidation of 3-chlorothiophene (CT) in mixed electrolytes of boron trifluoride diethyl etherate (BFEE) and trifluroacetic acid (TFA). The oxidation potential of 3-chlorothiophene in pure BFEE was measured to be only 1.54 V versus SCE. This value is much lower than that determined in neutral medium (2.18 V vs. SCE). The addition of TFA to BFEE can further decrease the oxidation potential of the monomer. The oxidation potential of CT in the mixed electrolyte of BFEE containing 30% TFA (by volume) was found to be as low as 1.16 V (vs. SCE). PCT films with the highest quality were obtained from the media of BFEE+10–15% TFA and they were characterized to have about 24–32 repeat units. The doping level and conductivity of PCT films also increased significantly by using the mixed electrolytes.