A new complex of Zn(II) and 5-Bromosalicylaldehyde thiosemicarbazone (5-BSAT) has been studied. In solution, the 5-BSAT reacts with Zn(II) to form a complex with the maximum absorbance at 381 nm. Zn(II) ion forms a 1:1 stoichiometric complex. The stability constant is 4.21x105. Formation of the complex was completed within 20 min at pH 6.8 and VDMF = 2 mL. Beer's law is obeyed over the range from 0.13 mg.L-1 to 0.39 mg.L-1 Zn(II) and the apparent molar absorptivity (ε) is 1.08×104 L.mol−1.cm−1. The complex has been formulated and characterized by mass spectrometry, FT-IR, 1H-NMR and 13C-NMR spectroscopies and IQmol program. The molecular formula of the complex is C8H8O2N3SBrZn. The ligand coordinated as an ONS tridentate dianion through the oxygen atom of the deprotonated phenolic OH-group, the azomethine nitrogen atom and the sulfur atom after deprotonation of the thiosemicarbazide residue in its thiol form. Based on these results, the 5-BSAT reagent applied to determination of Zn2+ in waste water samples and the complex showed an effective antimicrobial activity.