The variation of fenitrothion (MEP) concentration in the atmosphere was investigated after the aerial application of MEP for the control of pine sawyer beetles in Niigata City. In the applied area, MEP in air (C_A, μg/m³) was 5.2-100μg/m³ at maximal concentrations ; MEP was detected on 12d after the application. MEP was drifted to the points located 50-1000m from the applied area ; atmospheric MEP (C, μg/m³) were 0.19-1.1μg/m³ at maximal concentrations. C was mainly dependent on passing time after the application, wind direction, air temperature and the distance from the applied area. C_A (n=37) was represented by multiple regression analysis as log C_A=-1.007×log T+0.01290×cos θ-0.07283×υ^-1+6.033×log t-6.416 (γ²=0.736) where T (h), v (m), θ and t (°C) are passing time after the application, wind speed, wind direction (0⪈θ⪈180 ; θ=0 at a NW wind) and air temperature, respectively. C (n=122) was represented as log C=-0.3165×log T+0.2154×cos θ+0.6329×υ^-1+3.094×log t-0.2642×log D+0.2833×C_A-4.570 (γ²=0.763) where D (m) was 100 + the distance from the applied area.