Objective: To study effect and mechanism of gallic acid which extracted and separated from Dimocarpus longan stone on melanin synthesis of B16 cells. Method: Cultured mouse melanoma B16 cells in vitro

and treated with different concentrations of gallic acid in different time.Its effect on B16 cells proliferation was observed by MTT assay

content change of B16 cells melanin was determined to observe effects of gallic acid on melanin synthesis.By morphological observation

Hoechst 33342 staining and reverse transcription polymerase chain reaction (RT-PCR) were adopted to determine inhibition ways of gallic acid on B16 cells

and changes of tyrosinase expression in B16 cells.Mechanism of gallic acid on B16 cells melanin secretion was investigated. Result: Gallic acid had inhibitory effects on B16 cells significantly at the concentration range of 1-64 mg·L-1

half inhibiting concentration (IC50) of gallic acid on B16 cells growth were 32.29

22.47

18.68 mg·L-1 after treated for 24

48

72 h

respectively.Gallic acid significantly reduced melanin synthesis in B16 cells

and had positively related with concentration and acting time in a certain range.Inhibitory effect of gallic acid on B16 cells and melanin synthesis in different ways with different concentrations.At low concentrations (≤16 mg·L-1)

its inhibitory effect through apoptosis

at high concentration (>16 mg·L-1)

its inhibitory effect through cell directly killing way.When the concentration of gallic acid≤32 mg·L-1

it significantly reduced expression of tyrosinase in B16 cells. Conclusion: Gallic acid has obvious inhibitory effect on B16 cells and can reduce the content of melanin in B16 cells.Gallic acid has obvious inhibitory effect on tyrosinase expression in B16 cells.