Electrochemical studies of iron tetrasulfonated phthalocyanine (FeTsPc)immobilized on silica gel modified with titanium(IV) oxide were carried out in aqueous solutions. Cyclic voltammograms recorded in different supporting electrolyte solutions presented a redox process that became better defined under acidification. The position of the peak potentials (0.35-0.45 V vs SCE) and their invariance with solution pH indicated that these processes can be assigned to the Fe(II)TsPc/Fe(III)TsPc redox couple, with characteristics similar to those observed for FeTsPc adsorbed on graphite surfaces. The nature of the supporting cation in solution does not shift the midpoint potential (E(m)) of the redox process, when Li+, Na+, K+, and NH4+ are used. In contrast, the supporting anion has a strong effect, i.e., the E(m) shifts toward more positive values in the order ClO4->NO3->Cl->SO4=. Preliminary experiments indicated that the modified electrode presents catalytic activity for hydrazine oxidation in neutral solution.