Abstract: The ＥＣ５０(50% inhibitory growth concentration) values of nitrobenzenes were determined for population growth endpoint of escherichia coli and bacillus subtilis. Quantitative structure activity relationships (QSARs) were developed with negative logarithm of ＥＣ_５０(-lg ＥＣ _５０) in mole liter, as the dependent variable and six molecular descriptors lg　Ｐ, ¹X^Ⅴ , I, ^１Ｋa, ∑σ^－　and E_{LUMO as the independent variables. By means of multiple linear regression analysis, two equations were obtained, Ｅscherichia coli: -lg　ＥＣ^５０＝1.575+0.522lg　Ｐ+0.332I+0.341∑σ^－ , n＝27, r＝0.907, r^２=0.822, s=0.194, f=35.4. Bacillus subtilis：　 -lg ＥＣ５０＝0.744lg Ｐ+0.276I+0.230 ^１Ｋa+0.179ELUMO－0.928, n＝26, r＝0.964, r^２=0.928, s=0.113, f=68.1． The equations were used to estimate ＥＣ５０ for seven analogues and some toxicity mechanism was also discussed.}

Key words: escherichia coli, bacillus subtilis, nitrobenzenes, ＥＣ_{５ ０}, QSARs