Abstract: The toxicity of N-503 on wheat appears evidently in the seedling stage and becomes gradually less and little from the jointing stage to the mature stage. However, the symptom of damage is based upon the concentration of N-503 used. The concentration is better to keep below 50ppm. The effect of N-503 on rice is similarly to wheat, but the amount of residue in rice is more apparently than that in wheat. Chlorobenzene in the mixed sewage is also shown some damage symptom to rice.