some mg(11) complex of dibasic tridentate Schiff base ligands derived from aldehydes and orthoaminophenol have been synthesized and characterized by some physico-chemical studies; elemental, spectral (IR,UV,NMR) magnetic and conductance analyses. Dimeric tetrahedral geometry for the prepared complexes has been proposed. The antibacterial activity of the prepared complexes was also studied against some gram positive and gram negative bacterial.