The CeO2-SnO2/rGO was synthesized and used for modification of glassy carbon electrode (GCE) to measurement of Tramadol (Tra), Codeine (Cod) and Caffeine (Caf). Electrical impedance spectroscopy (EIS) techniques showed that CeO2-SnO2/rGO/GCE has the lower electron transfer resistance (Rct) (63 Ω) in comparison to GCE (223 Ω) and was suitable for electrochemical applications. The synthesized nanomaterials were investigated by some methods such as Transmission electron microscopy (TEM), X-ray Diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The pH value was investigated in the range of 5.5 to 9.5 which the best signal was obtained at pH=6.5. At the CeO2-SnO2/rGO/GCE three oxidation peaks appeared at 0.755, 1.05, and 1.412 V with Ipa= 22.1, 78.4 and 69.49 µA for Tra, Cod, and Caf and the peaks separation of ΔEp (Tra-Cod)=295 mV, and ΔEp (Cod-Caf)=362 mV in the potential region 0.4-1.6 V. In optimum condition, a dynamic range of 0.008-10 μM and 10-270 μM for Tra, 0.01-12 μM and 12-260 μM for Cod, 0.01-14 μM and 14-260 μM for Caf with the detection limit of 0.0056, 0.0053, and 0.0055 μM for of Tra, Cod and Caf, respectively, were obtained. Investigation of effect of scan rate (25 and 300 mV/s) shows that the electrode process was diffusion-controlled. Interference studies show that Li+, Na+, K+, Cl-, Ca2+, Uric acid, Ascorbic acid, Morphine, sucrose, and glucose have no effect on the oxidation current of the analytes. Finally, The presented electrochemical electrode was applied for the measurement of Tra, Cod and Caf in urine and human plasma spiked samples.