A novel series of quaternary ammonium cationic derivatives based on tetrapyridyl-porphyrin was synthesized.All the compounds were evaluated for their in vitro antibacterial activities against S.aureus,E.coli and P.aeruginosa,and antifungal activities against C.albicans,where microorganisms were exposed and unexposed to the irradiation.The results revealed that some of these compounds,especially,3a and 4a displayed satisfactory antibacterial activity against Gram-positive bacteria S.aureus and moderate antifungal activity against C.albicans.Unfortunately,Gram-negative bacteria P.aeruginasa was resistant to all compounds.The antimicrobial activity was found to be sensitive to the functional groups attached on the aromatic ring and the complex metal in the porphyrin ring,and decreased with the increase of electron-withdrawing capability of the functional groups.These preliminary results suggested that the remarkable antibacterial efficiency against S.aureus makes these substances promising antimicrobial agents. A novel series of quaternary ammonium cationic derivatives based on tetrapyridyl-porphyrin was synthesized. All the compounds were evaluated as their in vitro antibacterial activities against S. aureus, E. coli and P. aeruginosa, and antifungal activities against C. albicans, where microorganisms were exposed and unexposed to the irradiation. The results revealed that some of these compounds, especially, 3a and 4a exhibited satisfactory antibacterial activity against Gram-positive bacteria S. aureus and moderate antifungal activity against C. albicans. Unfortunately, Gram-negative bacteria P .aeruginasa was resistant to all compounds. The antimicrobial activity was found to be sensitive to the functional groups attached on the aromatic ring and the complex metal in the porphyrin ring, and decreased with the increase of electron-withdrawing capability of the functional groups. preliminary results suggested that the remarkable antibacterial efficiency against S.aureus makes These substances promisin g antimicrobial agents.