The insecticide p-nitropheny diethyl thiophospate is alse known by the symbol E.605 and a legion of trade names including “parathion”. The insecticide is widely used in agriculture, but it is highly toxic and now clear that parathion behaves like a cholinergic drug by inhibiting the enzyme cholinesterase. In order to know acute toxicity and the changes of glucose concentrations and activity according to time lapsed in female mice given orally single with the half dose to $LD_{50}$ of parathion, glucose contents and cholinesterase activities in serum as well as cholinesterase activities in whole brain and spinal cord were investigated, otherwise median lethal dose ($LD_{50}$) of parathion given orally against female mice was determined. The results obtained were summerized as follows ; 1. $LD_{50}$ value of parathion given orally to female mice was 7.1mg/kg(95% confidence limits, 3.8-13.1mg/kg) 2. The inhibition rate of cholinesterase activities in serum of parathion-administrated mice according to time lapsed were peakly decreased to 61% after 30 minutes in comparison to control group, but activities were completely recovered after 48 hours. 3. The inhibition rate of cholinesterase activities in whole brain of parathion-administrated mice according to time lapsed were peakly decreased to 49% after 2 hours in completely recovered after 24 hours. 4. The inhibition rate of cholinesterase activities in spinal cord of parathion-administrated mice according to time lapsed were peakly decreased to 57% after 2 hours in comparison to control group, but activities were completely recovered after 48 hours. 5. The changes of glucose contents in serum of parathion-administrated mice according to time lapsed and in directly after death due to parathion poisoning were no significantly difference.