A facile and sensitive electrochemical method was introduced to simultaneously determine acetaminophen (AAP) and its degradation product (p-aminophenol, PAP) on ultrathin poly (calconcarboxylic acid, CCA) film modified glassy carbon electrode (GCE). The results exhibited the poly-CCA modified GCE remarkably increased the peak currents of AAP and PAP oxidation. The poly-CCA modified GCE was utilized to electrochemically detect the individual or the mixture of AAP and PAP by cyclic voltammetry (CV) or differential pulse voltammetry (DPV) methods. Factors or conditions can make a distinct contribution to their shapes and separation of these two analytes. Results showed that under the optimal condition, the peak potential of AAP and PAP was well separated and the peak potential difference between them was reached to 250 mV at a scan rate of 100 mV s(-1) in DPV. The peak currents of AAP and PAP oxidation increase linearly with the respective concentrations. This method has been successfully applied to the detection of AAP and trace PAP in acetaminophen tablets. This assay has also been successfully applied in the pharmacokinetic study of AAP in vivo through intragastric administration of acetaminophen tablets to SD-rats. (C) 2011 Elsevier Ltd. All rights reserved.