Abstract: Quantitative toxicity-structure relationship of O-ethyl O-aryl N-isopropyl thionophosphor-amidates was studied by the determination of their hydrophobia, electronic and hydrolytic parameters as well as their acute toxicilies towards rats. From our experimental results it seems possible that the action between organo-phosphorous toxin and receptors may include dipole interaction. According to the QSAR of our experiment, the compound with low acute toxicity may be obtained when the molecular dipole moment is small and hydrophilicity is high.