A simple, sensitive and specific spectrophotometric method has been developed for the determination of manganese (II) in benzene. The metal ion reacts with 2-hydroxy-4-n-butoxy-5-bromo propiophenone thiosemicarbazone (HBBrPT) forming a dark yellow coloured complex in the pH range 7.0-11.0. The complex shows maximum absorption at 440 nm. Beer's law is obeyed in the range 2.74-6.86 µg/ml. The molar absorptivity and Sandell's sensitivity are found to be 5229 l mol^-1 cm^-1 and 0.0105 µg cm^-2, respectively. The solid complex have been isolated and characterized on the basis of elemental analysis, UV, IR, NMR and Mass spectra. HBBrPT is found to be a selective and strong chelating agent for manganese. The results deduced from Job's method of continuous variation, the mole ratio and the slope ratio method showed that metal: ligand ratio in the complex to be 1:2. The stability constant of the complex found to be 1.92 X 10⁷. The free energy change for the complex formation reaction is found to be -10.158 K cal/mole at 32^oC. The complex is fairly stable for about 24 h and up to 55^oC.