Seven transition metal complexes of Mn2+, Ni2+, Co2+, Cu2+ and Zn2+ with 3-aminopyridine (3-APy) as ligand have been synthesized, characterized by different techniques and their antibacterial activities were studied. Molecular modeling calculations were performed using DMOL3 program in materials studio package which is designed for the realization of large scale density functional theory calculation (DFT). The quantum mechanical and chemical reactivity parameters such as chemical hardness, chemical potential, electronegativity, electrophilicity index and Homo-Lumo energy gap were obtained theoretically and were used to understand the biological activity of the prepared compounds. Some complexes were tested for their in -vitrocytotoxic activity in human lung cancer cell lines (A-549 cell line), and structure-activity relationships were established. In general, the coordination to Co2+ increased the cytotoxicity while the Ni2+ complexes show reduced cytotoxic activity compared to the metal-free 3-aminopyridine.