Abstract: There are two indices-lethal oral dose and actinity values of blood cholinesterase-to identificaie death of organic phosphorous poison in forensic medicine. But both of them have not yet got a celarcut idea or definition, so that there are difficulties in the work of identification. In order to estimate the value of them, these two indices were compared, and a the acetyl cholinesterase (AChE) is the target organ's substance, it was supposed AChE would be a more sensitive index. In the experiment, 80 female sprague-Dawley rates were divided into 4 groups with the oral dose of 38. 7, 44. 4, 51. 1 and 58. 7 mg/kg DDVP respectively, and their fatalty rate and blood ChE activity were recorded. The results were theat there was no significant difference of ChE activity values between doses but high significant difference ( P<0.01= between survival and death. It is indicated that it does have a lethal dose of ChE, which can be used into forensic identification. And after the indices compared, it is showed that the ChE are much more sensitive than the oral dose of DDVP, that is to say 3.9 times the efficiency of DDVP oral dose. The methods of estimation-the definite value and the suspect zone--have been discussed.