A growing body of evidence indicates that lysozyme plays a significant role as an indicator for many diseases and a drug for treatment of infections, ulcers and to study the spatial conformation, enzyme kinetics, and molecular immunology. Therefore, highly sensitive determination of lysozyme is necessary and vital in a wide variety of fields. In this work, we put forward a simple but effective strategy for colorimetric visualization of lysozyme based on iodide-responsive Cu@Au nanoparticles (Cu@Au NPs) as well as the iodide-catalyzed H2O2-TMB (3,3,5,5-tetramethylbenzidine) reaction system. Colorimetric detection is applied because of its simplicity, fast response for analysis, high detection limit, low costs and practicality. In our strategy, iodide is applied for the reason that it can induce an obvious color change of the Cu@Au nanoparticles solution from gray to red, along with the change of morphologies of the Cu@Au nanoparticles from irregular to spherical. Consequently, this phenomenon results in colorimetric signal variation of the iodide-catalytic H2O2-TMB system. What's more, by quite simple biomolecule modification on the Cu@Au nanoparticles surface, an all-purpose colorimetric platform is established for the accurate detection of lysozyme, which could lead to the change of Cu@Au NP concentration through molecular recognition. The results show that modified Cu-Au NPs successfully achieved a simple, selective, visualized, and ultrasensitive detection of lysozyme with a linear range from 10(-7) to 10(-3) M and a detection limit of 60 nM.