A glassy carbon electrode (GCE) modified with multi-walled carbon nanotube-cetyltrimethylammonium bromide-poly(diphenylamine) (MWCNT-CTAB-PDPA) composite film was constructed and used to determine chloramphenicol (CAP) levels in biological samples. Diphenylamine (DPA) was successfully electropolymerized onto MWCNT-CTAB modified GCE using cyclic voltammetry in 1 mM monomer solution and 5 M H2SO4. The surface morphology of the MWCNT-CTAB-PDPA film was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The results showed that the electrochemical reduction of CAP on the modified electrode was adsorption-controlled. The effects of scan rate, electrolyte solution, accumulation condition, and amounts of MWCNT and CTAB were optimized. Under optimized conditions, the electrode showed a linear response in the range of 1.0 x 1 0(-8)-1.0 x 10(-5) M (R-2 = 0.9997) and a detection limit of 2.0 x 10(-9) M. The sensor was successfully applied to determine the level of CAP in milk and honey samples. (C) 2014 Elsevier B.V. All rights reserved.