A highly sensitive melamine electrochemical sensor was successfully constructed by self-assembling based on the composite of chitosan with polyvinyl pyrrolidone-dispersed reduced graphene oxide (CTS-PVP-rGO), gold nanoparticles (AuNPs) and metal-organic framework MIL-101. The characterizations of modified materials and electrodes were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron dispersive X-ray (EDX) spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The results indicated that the sensor of MIL-101/AuNPs/CTS-PVP-rGO/GCE exhibited a high sensitivity and selectivity as well as a good stability and reproducibility for the determination of melamine since CTS-PVP-rGO or AuNPs could enhance the conductivity of the sensor greatly and MIL-101 could promote the adsorption of melamine on the surface of the modified electrode remarkably. At pH 7.0, the scan rate of 100 mV/s and the frequency of 50 Hz, the determination limit of melamine was as low as 5.00 × 10–11 mol/L with the linear range from 5.00 × 10–11 to 1.00 × 10–8 mol/L and the correlation coefficient (R) of 0.996. Based on the electrochemical behavior of melamine on MIL-101/AuNPs/CTS-PVP-rGO/GCE, the possible redox procedure of melamine was put forward. Furthermore, the sensor of MIL-101/AuNPs/CTS-PVP-rGO/GCE was applied to the determination of melamine in milk products and a satisfying result was obtained.