A di-orthometallated triphenyl phosphite iridium complex Ir(dttpit)(phen)Cl (dttpitH2 = tris (2, 4-di-tert-butylphenyl) phosphite, phen = phenanthroline), has been synthesied and characterized. The crystal structure was determined by X-ray crystallography. The photoluminescence spectrum of Ir(dttpit)(phen)Cl in CH3CN shows emission maximum at 528 nm. In 0.01 wt% PMMA films, its quantum yields and lifetime are 0.16 and 1.78 μs, respectively. The emission of Ir(dttpit)(phen)Cl at 528 exhibits 1393% enhance upon addition of Ag+ in CH3CN/H20. The ratio of Ir(dttpit)(phen)Cl responding to Ag+ is 1:1, and the limit of detection is 0.13 μM. Ir(dttpit)(phen)Cl is a highly selective chemosensor for Ag+ over other metal ions. The interaction between the chlorine atom and Ag+ is responsible for the highly selective and sensitive phosphorescent senor for Ag+.