A Static exposure was performed as per OECD Guidelines for the Testing of Chemicals, Number 203 and EC Directive 92/69/EEC C.1 Acute Toxicity for Fish with oxadiazon 25% EC. Limit test was conducted with two groups, each group containing ten freshwater fish, Poecilia reticulata, in the treatment group fish was exposed to oxadiazon 25% EC at 100 mg (active ingredient)/L (2005.2 mg/L) and concurrently a control was maintained. Fish were observed daily during the acclimatization period for mortality. After the exposure on day 0 the fish were observed for mortality and toxicity signs approximately at 3rd hour and 6th hour and then once daily at 24, 48, 72 and 96 hour. Based on the results of stability analysis of oxadiazon 25% EC in the exposure medium under test conditions, the test item was stable upto 96 hour exposure period. At 96 hour the recovery percentage was greater than 80%. During the main experiment physic chemical parameters such as pH, temperature, dissolved oxygen, hardness and conductivity were analysed in the exposure water. The temperature of the control and test item concentrations maintained in the range of 21.0°C-21.1°C during the 96 hour exposure period. All fish were normal during the acclimatization period. No mortality and toxicity sign were observed in fish exposed to 100 mg (active ingredient)/L and in control group. Length and body weight of ten fish were recorded prior to acclimatization and on completion of the experiment all surviving fish weight and length was recorded. Analytical dose verification of the test item in the exposure medium samples was carried out in the test item concentration of 100 mg a.i./L. The samples at 0 hour and 96 hour were analysed by HPLC. The mean measured concentration ranged between 90.76% and 90.72% of the nominal concentrations at 0 hour is 89.75% and 89.80% at 96h exposure period.