Abstract: In order to study organophosphorus pesticides dissipation rates under abiotic conditions, researchers showed laboratory observations on the fenitrothion photodegradation and its temperature dependence. The kinetics and thermodynamic of fenitrothion were studied at temperature range 20-50°C under the irradiation of ultraviolet light. The results showed that photochemical reaction of fenitrothion in organic solvents such as acetone under UV light could be well described by the first kinetic equation and the photodegradation efficiency increases with increasing temperature in the range 20-50°C. The photodegradation rate constant of fenitrothion were 0.01, 0.03, 0.08 and 0.38 h-1 and the corresponding half-lives were 31.6, 29.4, 9.6 and 7.8 h at 20, 30, 40, 50°C, respectively. The apparent activation energy was calculated to be 10.9 kJ mol-1. Thermodynamic parameters of activation were also assessed for the degradation process.