Abstract: HPLC-MS/MS was applied to the simultaneous determination of 1-naphthol and 2-naphthol in hair dye. The sample was extracted with a mixture of methanol and water (1+1), and purified on ProElut PLS solid phase extraction column. The eluate was evaporated to dryness by N2-blowing, and the residue was dissolved with and made up to 1 mL of methanol and separated by using Agilent ZORBAX SB-C18 column (2.1 mm×150 mm, 3.5 μm), and mixtures of acetonitrile and water in different ratio as mobile phase for gradient elution. Negative electrospray ionization as well as multiple reaction monitoring mode were used in the detection. Linearity ranges of 1-naphthol and 2-naphthol were found same between 0.05-10.0 mg·L-1, with their detection limits (3S/N) of 0.05 mg·kg-1, and lower limit of determination (10S/N) of 0.2 mg·kg-1. The proposed method was used in the determination of the 2 compounds in substantial samples, and recovery was tested by addition of mixed standard solution to blank samples giving results of recovery in the range of 82.5%-102% with values of RSD′s (n=10) in the range of 6.3%-11%.