Colorimetric recognition and sensing of sulfide with high selectivity by virtue of glutathione-modified gold nanoparticle (GSH-AuNP) is presented. The assay is developed based on a specific anion-for-molecule ligand exchange reaction, through which sulfide replaces glutathione self-assembled on the AuNP. The unique feature of the GSH-AuNP probe makes it a novel colorimetric sensor for sulfide.