A nanocomposite based on multiwalled carbon nanotubes (MWCNT) modified with antimony nanoparticles (SbNPs) was synthesized chemically and has been applied to construct an electrode using carbon paste as substrate (SbNP-MWCNT). The developed electrode was applied for the determination of trace heavy metals Pb²⁺ and Cd²⁺ by square-wave adsorptive stripping voltammetry. The results were compared with those obtained by related electrode configurations such as Sb-film carbon paste electrode (SbF) and Sb-microsphere-multiwalled carbon nanotube composite carbon paste electrode (Sbmicrosphere-MWCNT) in model solutions. The analytical signals for Pb²⁺ and Cd²⁺ decreased in the order I_{Sb-nanoparticle} > I_Sb-film > I_{Sb-microsphere}, indicating that the size of the Sb particles on the coating layer influenced the oxidation current signals of Pb and Cd. The detection limits of the analytes were 0.77 μg L⁻¹ and 0.65 μg L⁻¹ for Cd²⁺ and Pb²⁺, respectively. The designed electrode was tested for the determination of target ions in wheat flour certified reference material, and the results compared well with those obtained by inductively coupled plasma time-of-flight mass spectrometry, showing satisfactory performance of the composite electrode.