Porphyrins and their derivatives have amazing optoelectronic properties that recommend them as sensitive compounds for sensors formulations [1]. Metalloporphyrins act usually by axial coordination to the central metal ion and can recognize different types of anions [2].  Pt(II) 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin was synthesized by metalation reaction of the porphyrin base, characterized by AFM, SEM, UV-vis, FT-IR and 1H-NMR spectroscopy and was used in UV-vis spectrometric determination of triiodide ion.  Accurate determination of triiodide ion is important in various clinical tests and in chemical analysis, amongst which we mention here the detection of ascorbic acid and hydroquinone in drugs.  By adding increased concentrations of I3‒ solutions to a certain solution of Pt(II)-porphyrin and monitoring the process by UV-vis spectroscopy, a perfect linear dependence was obtained between the intensity of absorption and the triiodide ion concentration in the range of 10-7-10-9M, as depicted in Figure 1. The limit of detection of 10-9 M for triiodide anion makes this method a suitable, fast and not-expensive one for clinical tests.  Acknowledgments: Authors are grateful to UEFISCDI because this work has been partially supported by 76 PCCDI Project belonging to PNIII-Future and Emerging Technologies and partially by Programme 3 - 2018 from Institute of Chemistry Timisoara of Romanian Academy. This work is dedicated to Romanian Centennial Anniversary (1918-2018).