A simple, rapid colorimetric detection method for Pb²⁺ in aqueous solution has been developed by using sodium thiosulfate (Na₂S₂O₃) and hexadecyl trimethyl ammonium bromide (CTAB) modified gold nanoparticles (Au NPs). Na₂S₂O₃ was added into the Au NP solution and thiosulfate ions (S₂O₃²⁻) were adsorbed on the surface of the Au NPs due to electrostatic interactions. Au atoms on the surface of the Au NPs were then oxidized to Au(I) by the O₂ that existed in the solution in presence of thiosulfate. The addition of Pb²⁺ (the final concentration was lower than 10 μM), accelerated the leaching of the Au NPs, and Pb–Au alloys also formed on the surface of the Au NPs. There was an obvious decrease in the surface plasmon resonance (SPR) absorption of the Au NPs. The lowest concentration for Pb²⁺ that could be detected by the naked eye was 0.1 μM and using UV-vis spectroscopy was 40 nM. This is lower than the lead toxic level defined by the US Environmental Protection Agency (US EPA), which is 75 nM. In this method, CTAB, as a stabilizing agent for Au NPs, can accelerate the adsorption of S₂O₃²⁻ on the surface of the Au NPs, which shortened the detection time to within 30 min. Moreover, this detection method is simple, cheap and environmentally friendly.