Abstract: Due to the industrial and medical importance of lysozyme (LZ), the LZ detection techniques have received more and more attention. Herein, we developed a simple colorimetric method for rapid LZ detection using citrate-capped gold nanoparticles without any further surface modification. The well-dispersed gold nanoparticles in aqueous solution were induced to aggregate in the presence of LZ, which led to a visible color change from red to blue. The concentration of LZ can be determined by monitoring with bare eye or a UV-vis spectrometer. The linearity was observed between the absorbance ratio (A625/A525) and the LZ concentration in the range of 10 to 100 nM. The lowest detectable concentration of LZ was 10 nM. The feasibility of the developed method was evaluated by determination of LZ in egg white in combination with magnetic solid phase extraction.