>Magister Scientiae - MSc / This thesis reports on the syntheses of complexes of (arene) ruthenium (II) isoniazid Schiff base ligands for antimicrobial studies. Isoniazid Schiff base ligands; isonicotinyl acid (2-hydroxy-5- methyl-benzilidene)-hydrazide (L1), isonicotinyl acid (2-hydroxy-5-methoxy-benzilidene)- hydrazide (L2), isonicotinyl acid (-5-chloro-2-hydroxy-benzilidene)-hydrazide (L3), isonicotinyl acid (-5-bromo-2-hydroxy-benzilidene)-hydrazide (L4), isonicotinyl acid (2-hydroxy-5-nitrobenzilidene)- hydrazide (L5) were prepared by condensation reaction under reflux from equimolar amounts of isioniazid, which is an amine, with five different aldehyde moieties. Ruthenium (II) complexes of these isoniazid Schiff base ligands (C1 - C5) were prepared in an ethanolic solution under reflux and inert atmosphere at 60°C using Schlenk techniques. Fourier transform infrared spectroscopy (FTIR), ultraviolet – visible spectroscopy, thermogravimetric analysis, nuclear magnetic resonance and elemental analysis were the characterization techniques that confirmed the successful preparation of the ligands. All the ligands spectra displayed the imine functional group peak which confirmed the successful preparation. The ligands L1 – L5 and the complexes C1 – C5 were subjected to similar characterization techniques which further confirmed the successful syntheses and the coordination of metal and ligand by displaying a shift in their respective imine peaks and transitions values. All the synthesized compounds were subjected to a standard antimicrobial test using three microorganisms, Staphylococcus aureus, Methicillin resistant Staphylococcus aureus and Pseudomonas aeruginosa. Out the ten compounds tested, only ligand L5 gave the best results against Staphylococcus aureus.