Abstract: A method of UHPLC-MS/MS for the determination of 4 nitrosamines, including NNK, NNN, NAB and NAT, in tobacco was proposed. The sample was extracted with 0.1 mol·L-1 ammonium acetate solution by homogenization, after centrifugation, the supernatant was taken and separated on Waters Acquity UPLC BEH C18 (2.1 mm×100 mm, 1.7 μm) column, using the mixed solution of acetonifrile and 0.01 mol·L-1 ammonium acetate mixed in the different ratios as mobile phase for gradient elution. The contents of 4 nitrosamines were determined by MS/MS. The positive electrospray ionization and the multiple reactions monitoring mode were used in the detection. The isotope internal standard method was used to quantification for the 4 nitrosamines. Detection limit (3s) of NNK, NNN, NAB and NAT found were 0.06, 0.17, 0.15, 0.053 μg·L-1 respectively. The proposed method was applied to the analysis of tobacco samples, giving values of recovery in the range of 92.1%-104%. Values of intra-day and inter-day RSD′s (n=7) were found in the ranges of 2.7%-3.3% and 3.5%-4.2% respectively.