The specific colorimetric detection of Hg 2+ in the context of interference from coexisting metal ions in aqueous solutions is a challenge. Therefore, a series of easy-to-make Hg 2+ colorimetric chemosensors S1∼S3, bearing thiourea moiety as binding site and nitrophenyl moiety as signal group, were designed and synthesized. Among these sensors, S3 showed excellent colorimetric specific selectivity and high sensitivity for Hg 2+ in DMSO and DMSO/H 2 O binary solutions. When Hg 2+ was added to the solution of S3, a dramatic color change from brown to colorless was observed, while the cations Ca 2+ , Mg 2+ , Cd 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Pb 2+ , Ag + and Cr 3+ did not interfere with the recognition process for Hg 2+ . The detection limits were 5.0 × 10 −6 and 1.0 × 10 −7 M of Hg 2+ using the visual color changes and UV–vis changes respectively.