An electrochemical sensor was developed for the determination of synthetic food color, sunset yellow (SY), based on the electrocatalytic properties of multiwalled carbon nanotube and gold nanoparticle (MWCNT/AuNP) composite. The glassy carbon electrode (GCE) modified with MWCNT/AuNP nanocomposite film exhibited excellent electron transfer ability toward the oxidation of SY with high sensitivity and stability. A pair of well defined quasi-reversible cyclic voltammetric peaks were observed with the formal potential (E-0' = -108 mV) vs. Ag/AgCl in phosphate buffer solution (PBS). Various kinetic and thermodynamic parameters of the redox reaction such as standard heterogeneous rate constant (k(s) = 7.944 x 10(-1) s(-1)), electron transfer coefficient (alpha = 0.487), number of electrons (n = 1) exchanged and free energy of activation (Delta G) were calculated. Under optimum conditions, the nanocomposite film modified electrode showed a linear response in the range from 1 x 10(-6) to 1 x 10(-5) M, with a limit of detection 4.03 x 10(-8) M. Analytical application of the developed sensor for quantitative determination of SY in commercially available soft drink samples were discussed. (C) 2014 The Electrochemical Society. All rights reserved.