A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), was developed for simultaneous determination of 3-amino-3-azabicyclo[3, 3, 0]octane (aminoheterocycle) and 3-azabicyclo[3, 3, 0]octane (azabicycle)in gliclazide bulk drug. The optimal conditions of CZE-AD were 50mM borate solution (pH 9.0) as running buffer, 14kV as separation voltage and 0. 95V (versus SCE) as detection potential. Under the selected optimum conditions, the two analytes could be perfectly separated within 9 min. The linearity range of aminoheterocycle was from 1.0×10−6 to 1.0×10−3M and that of azabicycle was from 2.0×10−6 to 1.0×10−3M. Their detection limits were 5.0×10−7 and 1.0×10−6M, respectively, (S/N=3). This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 2% for both migration time and peak current. It has been successively used for the determination of these two analytes in gliclazide bulk drug, and the assay results were satisfactory. 2005 Elsevier B. V. All rights reserved.