Four metal-azo chelate complexes of Co(III), Ni(II), Cu(II) and Zn(II) have been synthesized from the azo ligand 1- [(6-Methyl-2-benzothiazolyl)-azo]-2-naphthol-4-sulfonic acid (BANS) and characterized by elemental analysis, spectral ( Mass, IR , and UV–Vis for azo ligand ), magnetic moment measurements and molar conductance studies. The electronic absorption spectra and magnetic susceptibility measurements of chelate complexes indicate octahedral geometry for all prepared complexes. The important infrared (IR) spectral bands corresponding to the active groups in the ligand and its solid complexes under investigation were studied and implies that (BANS) is coordinated to the metal ions in a mono negative tridentate manner. Finally the invitro biological screening effects of this azo ligand and its chelate complexes were tested against the bacterial species Staphyolococus aureus, Enterococcus, Streptococcus viridians, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumonia and fungal species Aspergillus niger and Aspergillu flavus by well diffusion method. The antimicrobial activity data showed that chelate complexes are more than of the free ligand.