Objective  To synthesize novel cationic porphyrin derivatives and investigate the photodynamic antimicrobial activities of these new compounds. Methods  Tetrapyridyl-porphyrin obtained from condensation reaction was reacted with a series of benzyl halides to get 10 novel cationic porphyrin compounds. The photodynamic antimicrobial activities of these new compounds in vitro against S. aureus

E. coli

P. aeruginosa

and C. albicans were evaluated respectively using twofold serial dilution technique. Results  Ten new ca-tionic porphyrin derivatives and their metal compounds were obtained. All these 10 compounds displayed satisfactory photodynamic antibacterial activity against Gram-positive bacteria

S. aureus

especial compounds 3a and 4a with MIC

80

at 2 and 0.5  μg/ml respectively

and showed moderate photodynamic antifungal activity against C. albicans. Unfortunately

their photodynamic antibacterial activities against Gram-negative bacteria E. coli were very weak

and P. aeruginosa was resistant to all compounds. The antimicrobial activity was decreased with the increase of electron-withdrawing capability of the functional groups attached on the aromatic ring. Conclusion  These preliminary results suggest that the remarkable antibacterial efficiency against S. aureus make these substances promising microbial agents.