Antibacterial action of Benzalkonium saccharinate on grampositive and negative bacteria was studied in vitro. Excellent bacteriostatic and bacteriocidal activity was found in it against these bacteria; grouth of which was sufficiency inhibited by such minimum concentation of the drug as 0.78∼25.0g/ml. However, addition of bovine serum to the media inflenced slightly the activity of Benzalkonium Saccharinate.