Abstract: Diphacinone is widely used in rodent control within recent years.But its susceptibility and tolerance were insufficiently studied.The present paper deals these two problems with three common rodents, the striped field mouse, Apodemus agarius, the yellowbreasted rat, Rattus flavipectus, and the sewer rat, Rattus norvegicus.The toxicities were different to the three rodents.the LD50 were 1.06±0.65 mg/kg for the field mouse, 18.39±11.28mg/kg for ythe ellow-breast rat, and 0.25±0.14mg/kg for the sewer rat, Individual differences were found to be so obvious that they varied from 16 to 512-fold. Most of the animals were dead within 7 days after test.The un-dead animals were undergone the tolerance tests, the LD50 were 72.41±37.34mg/kg for the field monse 187.40±79.44mg/kg for the yellow-breest rat, and 1.27±0.21mg/Jcg for the sewer rat, The tolerance to the pesticide, diphacinone, increased so tremendously.In deratization, we tuggested that the diphacinone must be used in low concentrotion and the poisonous baits should be placed in man piles of small quantity and once during a control.