The abnormal filament formation of Sal. typhi was observed on penicillin containing nutrient agar in 1u/ml. Characters of the filament cells were compared with normally harvested cells in the view points of oxidative activities to some substrates, acid agglutinating property, glucosamine content and serological properties. No difference was observed about the oxidative activities, the glucosamine content and the serological properties. With respect to the acid agglutinating property, as comparsed with the normal cells, the filament cells exhibited a property to agglutinate in broader PH range.