Coordination compounds play vital roles in biology, biochemistry and medicine. Thus, synthesis and study of new mixed ligand complex is very important. In this study a new Co (II) mixed ligand complex was synthesized using 1, 10-phenanthroline and acetonitrile as ligands. The complex was characterized by solubility test, conductivity and melting point measurement and physico-chemical (ICP-OES, FTIR, and UV-Vis.) methods. Both ligands were coordinated with the metal and form octahedral complex. The complex was evaluated for its activities in vitro against two Gram positive and Gram negative bacterial pathogens. The complex showed significant activities on the gram negative species. Key terms: mixed ligand complex, Co (II) chloride salt, 1, 10-phenanthroline, acetonitrile, and antimicrobial activity.