In this work, trimetallic PtAuRu nanoparticles were synthesized by a facile one-pot method and glassy carbon electrode (GCE) modified with this trimetallic catalyst was used to detect caffeic acid (CA). Particularly, visible light illumination was introduced to assist the electrochemical assay and satisfactory results were achieved. The linear range obtained from differential pulse voltammetry (DPV) analysis was wide from 0.0087 mM to 16.6 mM. The obvious improvement of the response current towards CA is probably because of the surface plasmon resonance (SPR) effect of Au in the as-synthesized nanoparticles. These results indicate valuable potential of light illumination in enhancing the performance of metallic nanocomposites-based sensors in electrochemical detection.