The residual amount of fumigant was measured over time after fumigation on pine wilt disease infected Pinus koraiensislogs in the forests of Yeoncheon and Pocheon. Dimethyldisulfide (DMDS, 99.6%) was treated in large scale fumigation(100m3) in Yeoncheon and measured after removing tarpaulin cover in the 2 weeks of fumigation. DMDS was detectedat the highest concentration of 77.9 mg/kg in the 2nd week of treatment and decreased to 0.6 mg/kg in the 24th week.Metam-sodium (25%) was treated in small scale fumigation (1m3) in Pocheon and the amount of methylisothiocyanate(MITC) was measured after removing tarpaulin cover at each time of investigation. MITC was detected at the highestconcentration of 72.0 mg/kg in the 2nd week of treatment and then decreased to 7.0 mg/kg in the 24th week. However,unlike DMDS, MITC in the 12th week was detected at high concentration similar to the 1st week, indicating that thecontinuity of the sealing with tarpaulin would have a decisive influence on the residual amount change in fumigated logs.