Abstract Introduction Single photon emission computed tomography (SPECT) imaging of the serotonin transporter (SERT) in the brain is a useful tool for examining normal physiological functions and disease states involving the serotonergic system. The goal of this study was to develop an improved SPECT radiotracer with faster kinetics than the current leading SPECT tracer, 123 IADAM, for selective SERT imaging. Methods The in vitro binding affinities of (2-(2′-((dimethylamino)methyl)-4′-iodophenylthio)benzenamine) (FlipADAM) ( 1c ), were determined using Hampshire pig kidney cells stably overexpressing the serotonin, norepinephrine (NET) or dopamine transporter (DAT). Localization of 125 IFlipADAM ( 1c ) was evaluated through biodistribution and autoradiography in male Sprague Dawley rats, and the specificity of binding was assessed by injecting selective SERT or NET inhibitors prior to 125 IFlipADAM ( 1c ). Results FlipADAM ( 1c ) displayed a high binding affinity for SERT ( Ki =1.0 nM) and good selectivity over NET and DAT binding (43-fold and 257-fold, respectively). 125 IFlipADAM ( 1c ) successfully penetrated the blood brain barrier, as evidenced by the brain uptake at 2 min (1.75% dose/g). 125 IFlipADAM( 1c ) also had a good target to non-target (hypothalamus/cerebellum) ratio of 3.35 at 60 min post-injection. In autoradiography studies, 125 IFlipADAM ( 1c ) showed selective localization in SERT-rich brain regions such as the thalamic nuclei, amygdala, dorsal raphe nuclei and other areas. Conclusion 125 IFlipADAM ( 1c ) exhibited faster clearance from the brain and time to binding equilibrium when compared to 125 I2-(2′-((dimethylamino)methyl)-phenylthio)-5-iodophenylamine 125 IADAM ( 1b ) and a higher target to non-target ratio when compared to 125 I5-iodo-2-(2′-((dimethylamino)methyl)-phenylthio)benzyl alcohol 125 IIDAM ( 1a ). Therefore, 123 IFlipADAM ( 1c ) may be an improved SPECT tracer for imaging SERT.