Abstarct: In this dissertation, glassy carbon electrode was successfully modified with a thin film of 1,5-diphenylcarbazone and applied for the sensitive and selective voltammetric simultaneous determination of ascorbic acid (AA), dopamine (DA) and acetaminophen (AC). This study, shows that 1,5-diphenylcarbazone as a modifier was bounded to the electrode surface using cyclic voltammetry technique. The effect of several parameters including concentration of 1.5--diphenylcarbazone, type of electrolye, number of cycles, pH, type of buffer, volume of buffer, puls amplitude and scan rate on the electrochemical determination of analytical were studied and optimized. The linear dynamic range of the proposed method were 10-200, 0.5-20 and 0.5-20 µM for AA, DA and AC, respectively under optimum condititions. Under the optimum conditions, The detection limits were 2.80, 0.04 and 0.07 μmol L−1 for AA, DA and AC, respectively. The effects of interfering ions and other drugs were studied and it was found that due to the sensor selectivity, the sensor has least of interference from most of the common ions and drugs do not interfere in the determination of the analyte. The proposed sensor has been successfully used for the simultaneous determination of AA, DA and AC in AC and AA tablets, blood seroum and tab water.