Abstract: Quantitative structure-activity relationship(QSAR) of the toxicity of some chloro-anilines and their structures was studied based on some quantum chemical descriptors derived by B3LYP methods.The equation obtained by multiple regressions was proved by the S.E test that the model was satisfactory.The results show the toxicity of the chloro-anilines to photobacterium phosphoreum increases with the decrease of the energy of the lowest unoccupied molecular orbital(ELUMO) and the increase of the number of chlorine atoms.