The possibility of applying antimony-film modified glassy carbon electrode in sequential-injection analysis (SIA) was investigated with the objective of determining Pb(II) and Cd(II) by anodic stripping voltammetry (ASV). The conditions of antimony-film deposition concerning composition of the plating/carrier solutions, concentrations of Sb(III) and hydrochloric acid, effects of different supporting electrolyte salts, and plating potential were optimized. It was found that the antimony-film deposition on glassy carbon substrate in a sample solution consisting of 750μgL⁻¹ Sb(III), 0.5molL⁻¹ HCl at −1.5V (vs. Ag/AgCl/3molL⁻¹ KCl) yielded a modified electrode suitable for the determination of Pb(II) and Cd(II) at the μgL⁻¹ level. The reproducibility of the analytical signals was characterized by a relative standard deviation lower than 2.8%, and the calculated values of detection limits were 1.2μgL⁻¹ for Pb(II) and 1.4μgL⁻¹ for Cd(II). The presence of KSCN in the sample solution offers the possibility of detecting ions with more negative oxidation potentials like Zn(II), Mn(II) or Cr(III). The developed SIA-ASV procedure was compared with the commonly used batch method, and its applicability was tested on a spiked tap water sample.