Abstract: In view of the serious threat of organophosphorus pesticide (OPs) residues to the environment and human health, it is important to develop a rapid, sensitive and enzyme-free detection method to solve the problems of existing technologies that rely on biological enzymes, high cost and complex operation. In this study, gold nanostars (AuNS) were synthesized by seed-mediated growth method, and platinum nanoparticles were loaded on their surface to prepare AuNS/Pt nanocomposites (AuNS@Pt). The synthesized AuNS@Pt exhibited oxidase-like activity, whose catalytic mechanism was elucidated through kinetic analyses. Capitalizing on the inhibitory effect of OPs on the active sites of AuNS@Pt, we developed a novel colorimetric detection platform. AuNS@Pt could efficiently catalyze the oxidation of TMB to generate blue products (characteristic absorption peak 652 nm). The adsorption of OPs (dimethoate, omethoate, malathion) inhibited its catalytic activity. The absorbance value was linearly related to the concentration of OPs within a certain range, and the limit of detection were 0.015, 0.022 and 0.050 μg/mL, respectively. The recoveries of spiked cabbage samples ranged from 85.6% to 103.2%, with relative standard deviation below 5.18%, which was consistent with the results of gas chromatography-mass spectrometry. The proposed method provides a new strategy for the rapid detection of OPs and is suitable for practical application in complex matrix samples.