Ethephon is a plant growth regulator and is often applied in the process of fruit growth. It could result in considerable inhibition of cholinesterase in blood plasma and erythrocytes and is very harmful to human beings on excessive consumption. Nanocomposites from polyaniline and stannic oxide (SnO₂@PANI) were synthesized and developed as the electrode material for detecting ethephon. Herein, SnO₂ nanoparticles were prepared by the method of liquid phase precipitation. Afterwards, the as-prepared SnO₂ nanoparticles were mixed with the aniline polymerization system to form the SnO₂@PANI nanocomposite. The basic chemical components of the fabricated sensor were characterized in detail using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. It was demonstrated that the developed SnO₂@PANI nanocomposite exhibits good electrochemical performance with relatively low charge-transfer resistance. Compared with the pristine SnO₂ and PANI, ethephon preferred to adsorb onto the SnO₂@PANI nanocomposite surface because of the synergic interaction between the two components of SnO₂ and PANI. The electrochemical impedance spectra illustrated that the fabricated ethephon sensor had excellent sensitivity, with a detection limit of 4.76 pg mL⁻¹ within the range from 0.01 to 5 ng mL⁻¹. Moreover, the developed electrochemical biosensor exhibits good selectivity and stability. All of these good performances provide a promising tool to detect illegal food additives.