Abstract: GC-MS/MS with separation by liquid-liquid extraction was applied to the determination of 12 organochlorine pesticides in water. The sample was extracted with n-hexane. The DB-5MS column was used in GC separation and the multiple reaction monitoring mode was adopted in MS determination. Linear relationships between values of peak area and mass concentration of the 12 organochlorine pesticides were kept in definite ranges. Detection limits found were ranged from 0.002 to 0.032 μg·L-1 with lower limits of determination in the range of 0.008-0.128 μg·L-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 99.1%-126%, with RSD′s (n=7) in the range of 2.3%-9.3%.