The bacteriostatic action of trichlorophenoxy alkylene ammonium derivatives, 2(2,4,5-trichlorophenoxy) ethylene N-triethyl ammonium bromide; (2,4,5-TETB), 2(2,4,6-trichlorophenoxy) ethylene N-triethyl ammonium bromide; (2,4,6-TETB), 2,4,5-triphenoxy ethylene pyridinium bromide; (2,4,5-TEPB), and 2,4,6-trichlorophenoxy ethylene pyridinium bromide:(2,4,6-TEPB) were observed by Jackson and Finland s and Finland s and Pak s on Staphylococcus aureus, E. coli, Salmonella typhi, Shigella flexneri, and Bacillus subtilis, comparing with those of phenol and trichlorophenol. The following results were obtained. 1) Phenol is bacteriostatic in a concentration of 10^-3 for all above species. 2) Trichlorophenol is bacteriostatic in concentration of 10^-4 to 5 X 10^-5 for all above species(Table 7), 3) 2,4,5-TETB and 2,4,6-TETB are bacteriostatic in a concentration of 10^-4 and 5 X 10^-5 for Staphylococcus aureus, Salmonella typhi, and Shigella flexneri, but do not for E. coli and Bacillus subtilis(Table 8 and 9). 4) 2,4,5-TEPB and 2,4,6-TEPB are bacteriostatic in a concentrationof 10^-4 and 5 X 10^-5 only for Staphylococcus aureus among four species(Table 10 and 11).