This work describes an alternative method for benzoyl peroxide (BP) determination in pharmaceutical samples, using an amperometric sensor based on a carbon paste modified with (2,2′:6′,2″-terpyridyl) copper(II) chloride complex [Cu(terpy)Cl]Cl·2H2O. The sensor presented the best response in 0.10moll-1 phosphate buffer solution (pH 7.0) applying a potential of -50mV versus SCE. In the optimized conditions the sensor showed a linear response range for BP from 0.9 to 5.0μgml -1. The response time for this sensor was 0.5s. The paste presented a stability of at least 6 months at room temperature. The precision of the measurements was 4.5%, expressed in term of relative standard deviation (R.S.D.) for n=5. A detailed study was carried out, in order to investigate the sensor response for some compounds contained in pharmaceutical formulations, such as carboxypolymethylene (carbopol® 940), triethanolamine, propyleneglycol, hydroxyethylcellulose (natrosol®), and no interference was observed with these compounds. The applicability of the sensor for BP determination was evaluated in pharmaceutical preparations, obtaining recovery averages of 98±1%. © 2003 Elsevier B.V. All rights reserved.