The electronic structures of organic phosphate pesticide mols. have been calculated with CNDO/2 method. A new parameter CB is defind, which is the ratio of the net charge on atom P to the sum of bond orders of P = X and P-Y, the most weak ester bond in the mol. The CB values of mols. in the same series of organic phosphate can be used to characterize the electronic effects on the biol. activities of the mols. So that the relation of the biol. activities to the electronic structures of mols. was discussed on the basis of CB values.L

Key words: BIOLOGICAL ACTIVITY, ORGANO PHOSPHORUS COMPOUNDS, CNDO APPROXIMATION, ELECTRONIC STRUCTURE, PHOSPHATES