The carbon paste electrode is electrocatalytically active for dopamine, ascorbic acid and uric acid oxidation. The electrocatalytic oxidation current is developed from the anodic peak of the redox couple. Electrochemical impedance spectroscopy is applied to monitor the entire electrode modification process and supplies useful information as to the impedance changes on the electrode surface between each step. The surface morphology of the composite film is using scanning electron microscopy and atomic force microscopy, and cyclic voltammetry is used to measure the electroanalytical properties of the analytes. The sensitivity values of the carbon paste electrode are higher than those of the bare electrode. Finally, differential pulse voltammetry is used to detect the mixture of analytes at the carbon paste electrode. We simulate a more complex system when dopamine, ascorbic acid and uric acid are present simultaneously. The peak currents for the analyte mixture increased linearly with the analyte concentration. The detection limit of the carbon paste-modified electrode for ascorbic acid, dopamine and uric acid was 8.3 10-6 M, 1.5 10-6 M and 1.6 10-6 M, respectively