A novel glassy carbon composite electrode modified in bulk with mercuric oxide was developed for simultaneous determination of lead and cadmium using square-wave anodic stripping voltammetry. The hole-conductor material triphenylamine was used as the binder instead of paraffin oil for fabrication of this novel electrode, which exhibited very attractive electrochemical performance. The mercuric oxide was absorbed onto the surface of glassy carbon particles and was further electrochemically reduced to form a mercury film on the electrode surface. In the stripping analysis, the developed electrode yielded well-defined and separate peaks for the oxidation of lead and cadmium. Several parameters, such as the amount of mercuric oxide, deposition time, and deposition potential, were optimized to obtain the best stripping response. The linear range for both metal ions was from 0.5 to 50 µg L-1, and the detection limits for the determination of lead and cadmium were 0.08 and 0.05 µg L-1, respectively. The electrode was also applied to determine lead and cadmium in milk samples. Results showed that the milk samples contained low (µg L-1) levels of lead and cadmium. The proposed electrode was sensitive, reliable, and effective for the determination of trace heavy metals, which may hold great promise for routine analysis applications.