In this work, the complex of cobalt(II),[Co(Phen)2(Ad)(Ac)]Cl2was synthesized from 1,10-phenanthroline alone as well as from 1,10-phenanthroline , adenineand acetamide. The synthesis was checked using halide test,solublity test, molar conductance measurement, melting point measurment, and spectroscopic (ICP-OES, FT-IR, and UV-Vis) analysis andthe results indicated that the cobalt ion coordinated to the ligands give octahedral complex. The in vitro antibacterial activities were also investigated on two Gram-positive (Staphylococcus aureus(S. aureus) andStreptococcus pyogens (S. pyogens) and two Gram-negative Escherichia coli (E.coli) and Klebsiella pneumoniae (K. pneumoniae)) bacteria. These complexes showed wide-rangeactivities against even the most drug resistantKlebsiella pneumoniae. The percent activity index of [Co(Phen)2Ad(Ac)]Cl2 againstS. aureus, S. pyogens, E. coliandK. Pneumoniaeby -32.33%, -38.71%, -13.99%, and -29.90%, respectively. Keywords:Cobalt(II) salt, 1,10-phenanthroline, adenine, acetamide, mixed ligandcomplexes andantibacterialactivities