This chapter summarizes the recent advances in the electrochemical detection of toxic chemicals with the use of metal oxide-metal nanocomposites as the electrochemical sensing platform. The study of toxic chemicals was classified into the following five major groups: endocrine disrupting chemicals, pesticides and disinfectants, environmental pollutants, mycotoxins, and volatile organic compounds. Electrochemical (amperometric, voltametric, and impedimetric) sensor systems made up of metal oxide-metal nanocomposites are systematically reviewed. A metal oxide-metal nanocomposite as an entity provides augmented characteristics compared to the original constituents due to the synergism between the metal nanoparticles and the metal oxide derivatives. The resultant nanocomposites furnish an enriched active surface area, better adsorption ability, and improved electrocatalytic activity. As a result, the sensor systems not only engender subfemtomolar detection limits but also thrive in a widespread concentration range along with much better selectivity. Integration of nanocomposites with electroanalytical systems is extensively sought after to harvest various features, such as miniaturization, rugged instrumentation with no mechanical parts, portable on-site analysis, multiplex analysis, automation, tunable microprobes apt for in vivo analysis, etc., in the developed sensor systems. It is anticipated that this chapter will help electrochemists to deliberate innovative combinations of metal oxides and metal nanoparticles along with other advanced functional materials while constructing electrochemical sensor systems for on-site analysis of any necessary analyte. © 2021 Elsevier Inc. All rights reserved.