Four new Co(II), Ni(II), Cu(II) and Fe(III) chelates with synthesized azo Schiff base ligand (ASB) derived from Schiff base [salicylaldehyde and 2-aminothiophenol] with aniline were synthesized and characterized on the basis of various physicochemical methods including; CHNS elemental analyses, molar conductivity, magnetic moment measurements, infrared, electronic, mass and proton nuclear magnetic resonance spectra. The used techniques showed the formation of 1:1[M:L] ratio and confirm the geometrical structures of the azo Schiff base and its chelates. A square planar geometry was established for Ni(II) and Cu(II) chelates and octahedral structure for Co(II) and Fe(III) chelates. The corrosion inhibition of mild steel in 0.5M HCl using azo Schiff base as inhibitor has been studied at 30 0C. High inhibition efficiency (> 90 %) of azo Schiff base for acidic corrosion of steel was determined at its low concentration (3×10-4 M) by weight loss measurements.