The adverse effects that thiourea can induce in biological systems demand the development of new methods for its detection. In this work, we present a iridium(III) complex-based chemosensor (1) containing a recognition unit for thiourea. The reaction of the recognition unit with thiourea affects the long-lived excited states of the complex, leading to an enhancement of luminescence. Complex 1 showed a 3.3-fold enhanced luminescence in the presence of thiorea and a good linear relationship with thiourea ranging from 10 to 200 mu M, with a limit of detection (LOD) of 3.85 mu M. By using time-resolved emission spectroscopy (TRES), complex 1 could detect thiourea in the presence of interfering fluorescence. Moreover, complex 1 offers the capability to image thiourea in living HeLa cells. To our knowledge, complex 1 is the first iridium(III) complex-based sensor reported for imaging thiourea in living cells. (C) 2017 Elsevier B.V. All rights reserved.