A simple and sensitive electrochemical sensor based on Au nanoparticles/poly (L-arginine) modified carbon paste electrode (AuNPs/Parg/CPE) was constructed and utilized to determine cefotaxime. Scanning electron microscope (SEM) image showed that the L-arginine (L-arg) had been electropolymerized on the CPE and the immobilized Au nanoparticles (AuNPs) were spherical in shape. Fourier transform infrared spectra (FTIR) indicated that the poly (L-arginine) (Parg) film was successfully modified on CPE. Electrochemical impedance spectroscopy (EIS) and cyclic voltammogram (CV) illustrated the Parg and AuNPs efficiently decreased the charge transfer resistance value of electrode and improved the electron transfer kinetic between analytes and electrode. The electrooxidation of cefotaxime on the modified electrode was performed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The results showed the response current of cefotaxime at AuNPs/Parg/CPE increased 17 times than that of bare CPE. The calibration curve was linear over the cefotaxime concentration range of 0.01-100.0 mu M with a detection limit (S/N = 3) of 2.3 nM. This proposed method has been applied to determine cefotaxime in pharmaceutical formulations and human serum samples, and the results were satisfactory. (C) 2013 Elsevier B.V. All rights reserved.