A novel reversible phosphorescent sensor for Hg2+ based on a neutral iridium (III) complex Ir(TBT)2(pic) (TBT=2-thiophen-2-yl-benzothiazole, pic=picolinate) has been synthesized and characterized. Ir(TBT)2(pic) displayed relatively strong phosphorescent nearly centered at about 600 nm. Upon addition of acetonitrile (CH3CN) solution of Hg2+, the dichloromethane (DCM) solution of Ir(TBT)2(pic) gave a visual color change from orange to yellow and significant phosphorescent quenching. It can serve as a highly selective sensor for Hg2+ with naked-eye detection. The sensor allow determination of Hg2+ in the working range of 4.0 μM-12.0 μM with a detection limit of 1.04 μM. When mixing with Hg2+, Ir(TBT)2(pic) interacted with Hg2+ in a 1:2 stoichiometry via a coordination bond interaction between the sulfur atom and Hg2+. The phosphorescent chemosensor exhibited excellent selectivity and sensitivity for Hg2+ detection. The spectral response of Ir(TBT)2(pic) toward Hg2+ was proved to be reversible.