|Vitex trifolia L. has been used traditionally to treat various illnesses, such as inflammation, headache, migraine, and gastrointestinal infections. We analyzed and evaluated the composition of V. trifolia leaf oil. Based on the results, we isolated abietatriene from V. trifolia leaf oil and investigated the effect of V. trifolia leaf oil and its active compound abietatriene on melanogenesis in B16F10 melanoma cells. They significantly decreased melanin contents and melanogenic factors, such as tyrosinase, TRP-1, TRP-2, and MITF dose-dependently in both protein and mRNA levels. Protein and mRNA expressions were determined by Western blot analysis and quantitative real time RT-PCR. Findings indicate that V. trifolia leaf oil and abietatriene reduce melanogenesis by regulating the expression of melanogenic factors. These results suggest that V. trifolia leaf oil and abietatriene could comprise a useful therapeutic agent for treating hyperpigmentation and used as effective skin-whitening agents.