A sensitive Pb(II sensor was fahrirated osan) nanocomposite modified glassy carbon electrode (GCE). The Co3O4/rGO material was synthesized through in situ growth of Co3O4 nanoparticles (NPs) on GO and subsequent hydrazine reduction process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that Co3O4 NPs with a diameter of around 100 nm are attached on rGO sheets. The structures and compositions of Co3O4/rGO were further characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Many experimental parameters, such as pH value, deposition time and deposition potential were optimized. Under optimal conditions, the calibration plot for Pb(II), with data acquired at -0.556 V (vs. SCE) is linear in the concentration range from 1.0 to 200.0 nM. Combining the good conductivity and high surface area of rGO, strong Pb(II) adsorption ability of Co3O4 NPs, and excellent Pb(II) complex-forming ability of chitosan, the nanocompsite provides a sensitive Pb(II) senor with a detection limit of 0.35 nM. Moreover, the positively charged chitosan can interact with the negatively charged rGO to increase the stability of Co3O4/rGO nanocomposite. The hybrid nanocomposite Pb(II) senor provides new opportunity for vegetable analysis.