To develop a simple and sensitive colorimetric detection method for Pb2 + based on cysteine functionalized gold nanoparticles (Cys-AuNPs). AuNPs with a particle size of 13 nm were synthesized using sodium citrate reduction method and then functionalized with cysteine. Cys-AuNPs could be induced to aggregate immediately in the presence of Pb2 + through chelating ligand binding, which led to the colorimetric response of AuNPs, with changes in the position and strength of AuNPs characteristic peaks as well as the solution color. The experimental results indicated that a good linear relationship was found in the Pb2 + concentration range between 0.02 μ mol/L and 5 μ mol/L, and the limit of detection (LOD) was 0.01 μmol/L. The selectivity of this method was confirmed by comparison with the UV/Vis spectra of other divalent metal ions. The colorimetric method could be used in the actual application of Pb2+ detection.