Abstract: In this study the complexes of salicylaldehyde thiosemicarbazone with Pd, Cu and Ru were prepared. The prepared complexes were characterized by spectroscopic, element and thermal analyses and D.C. conductivity measurement. The antimicrobial activity of all the prepared compounds against gram-positive, gram-negative and fungi was studied. From these studies, it has been obtained that the ligand is bonded to the metals through O, N and S, but to palladium in [Pd(H2L2)]Cl2 only through N and O. Biological studies confirm that the organic effect on both gram-positive and gram-negative bacteria is very weak and their complexes have no effect on fungi, but Cu-complex has strong influence on both types of bacteria.