Developing rapid, efficient and highly sensitive sensing systems for organophosphorus (OPs) and organochlorine pesticides is important due to their potential damage to human health. Considering that Fe³⁺ ions were recently found to have much higher peroxidase-like activity than that of Fe₃O₄ magnetic nanoparticles, in this work, a novel and highly sensitive multi-catalytic sensing system has been successfully developed for OPs and organochlorine pesticides, on the basis of the color reaction of 3,3′,5,5′-tetramethyl benzidine (TMB) driven by Fe³⁺ ions, together with two enzymatic catalytic systems of acetylcholinesterase (AChE) and choline oxidase (CHO). Sub nM level limits of detection could be achieved for four tested OPs and organochlorine pesticides. Furthermore, several fruit/vegetable samples were successfully employed for evaluating this established sensing system.