Abstract A novel hexadentate nitrogen–sulphur donor [N 4S 2] macrocyclic ligand, i.e. 3,13-dithio-6,10,16,20-tetraoxo-8,18-dithia-1,2,4,5,11,12,14,15-octaazacyclocosane (L), has been synthesized. Cobalt (II) complexes of this ligand have been prepared and subjected to elemental analyses, molar conductance measurements, magnetic moment susceptibility measurements, mass, 1H NMR (Ligand), IR, electronic, and EPR spectral studies. On the basis of molar conductance, complexes may be formulated as [Co 2(L)X 2]X 2 [where X = Cl −, Br −, NO 3 − and NCS −] due to their 1:2 electrolytic nature in dimethylformamide (DMF). All the complexes are of the high spin type and are four coordinated. On the basis of IR, electronic and EPR spectral studies tetrahedral geometry has been assigned to all the complexes. The antimicrobial activities of the ligand and its complexes, as growth inhibiting agents, have been screened in vitro against several species of bacteria and plant pathogenic fungi.