A facile, cost-effective and sensitive colorimetric detection method for Pb(2+) has been developed by using glutathione functionalized gold nanoparticles (GSH-GNPs). The sensitivity and selectivity of detection were investigated in detail. The GSH-GNPs could be induced to aggregate immediately in the presence of Pb(2+), especially after the addition of 1 M NaCl aqueous solution. The Pb(2+) could be detected by colorimetric response of GNPs that could be monitored by a UV-vis spectrophotometer or even naked eyes, and the detection limit could reach 100 nM. The GSH-GNPs bound by Pb(2+) showed excellent selectivity compared to other metal ions (Hg(2+), Mg(2+), Zn(2+), Ni(2+), Cu(2+), Co(2+), Ca(2+), Mn(2+), Fe(2+), Cd(2+), Ba(2+), and Cr(3+)), which led to prominent color change. This provided a simple and effective colorimetric sensor (no enzyme or DNA) for on-site and real-time detection of Pb(2+). Most importantly, this probe was also applied to determine the Pb(2+) in the lake samples with low interference and high sensitivity.