The anodic electropolymerization of pyrrole 3 substituted by a pinacolborane moiety 1 yielded anion-sensitive conjugated polymer films. The effect of different halides (F-, Cl- and Br-) on the voltammetric response of poly(1) was examined in organic and hydro-organic media. Larger effects were observed in CH2Cl2, because of a weaker solvation of anions. In this solvent the system corresponding to the doping/undoping of poly(1) was shifted 450 and 175 mV towards less oxidizing potentials in the presence of F- and Cl-, respectively. In contrast, the polymer response was unchanged upon the addition of Br. These results were consistent with a greater affinity of the immobilized boronic ester groups for F-, which could be explained by the hardness of the Lewis base.