Schiff base ligand, (E)-methyl 6-acetamido-2-(5-bromo-2-hydroxybenzylideneamino)-4,5,6,7- tetrahydrobenzo[b]thiophene-3-carboxylate, was successfully prepared with condensation reaction. The newly obtained Schiff base used to synthesize five new complex, [FeLCl(H2O)2]∙1.5H2O, [CoLCl(H2O)2]∙2H2O, [NiLCl(H2O)2]∙H2O, [RuLCl(p-cymene)]∙3.5H2O and [PdLCl∙H2O]∙ 3H2O. From the magnetic and spectral data, the geometric structures of these complexes were found to be square planar and octahedral. The characterizations of ligand and complexes were done by FT-IR, UV-Vis, 1H and 13C-NMR, microanalyses, magnetic susceptibility, mass spectra and thermogravimetry analysis (TGA) and further were screened for antioxidant activities. Antioxidant properties of synthesized compounds were examined using different methods including total antioxidant activity, FRAP (ferric reducing antioxidant power), CUPRAC (cupric reducing antioxidant capacity) and DPPH (2,2-diphenyl-1-picrylhydrazyl). The Ru(II), Pd(II), Fe(II) and Co(II) metal complexes generally exhibited good antioxidant properties.