Poly(3-butylthiophene-co-3-bromothiophene) film was electrochemically deposited onto stainless steel electrodes from freshly distilled boron fluoride ethyl ether. The reactivity ratios of r(1) = 0.52 (for 3-butylthiophene) and r(2) = 0.95 (for 3-bromothiophene) were obtained by the Fineman-Ross method based on IR measurements. The results are very important for controlling the composition of copolymers. The poly(3-butylthiophene-co-3-bromothiophene) films are flexible with a tensile strength of 18.3 MPa. The conductivities of the copolymer films are in the range of 10(1)-10(-2) S/cm.