Abstract: This is the first time to investigate the chemical constitutes of Forsythia suspensa flower for tyrosinase-inhibition activity. First, different organs (flower,leaf,green Forsythiae Fructus and ripe Forsythiae Fructus) of F.suspensa  were tested for the tyrosinase-inhibition activity,and the F.suspensa flower showed concentration-dependent on the inhibition of tyrosinase activity.Second,different extracts of F.suspensa flower were also tested for the tyrosinase-inhibition activity,and the 95% ethanol extract displayed the best inhibition of tyrosinase activity.Then,five compounds were obtained from 95% ethanol extract by the activity-guided isolation method,and their structures were identified as forsythiaside A (1),rutin (2),(+)-pinoresinol-β-D-glucoside (3),(+)-pinoresinol monomethyl ether β-D-glucoside (4) and (+)-phillyrin (5),while compound 4was reported for the first time from F.suspensa flower.Four of them showed weak inhibition activity against tyrosinase but displayed obvious synergistic effect.The results implied that the 5 compounds were most likely to be the chemical substance foundation of the whitening effect of F.suspensa flower and its inhibitory effect was possibly produced by synergistic effect.

Key words: Forsythia suspensa flower, extraction and separation, tyrosinase inhibition, chemical substance, synergistic effect