Abstract: Soil sample was extracted with acetone, and the extract obtained was analyzed by LC-MS/MS. Agilent SB-C18 column (150 mm×4.6 mm, 5 μm) was used as stationary phase. Mixture of 0.05 mmol·L-1 NH4Cl in methanol (30+70) was used as mobile phase and electrospray ionization source with negative ionization mode as well as multiple reaction monitoring mode were used in the MS/MS analysis. Linear relationship between values of peak area and mass concentration of pentaeythritol tetranitrate (PETN) was kept in the range of 0.25-75 μg·L-1, with detection limit (3S/N) of 0.25 μg·kg-1. Tests for recovery were made by addition of standard PETN solution at 3 different concentration levels to samples of clay as matrixes, values of recovery found were in the range of 92%-97%, with values of RSD′s (n=6) in the range of 1.1%-2.4%.