Objective: The aim of the present study is to identify the toxic substances in Genkwa Flos extract which could induce human liver cell line L02 injury. Method: MTT assay was applied to assess human liver cell line L02 proliferation after incubation with Genkwa Flos extract. The chemical constituents in Genkwa Flos extract and their affinity with L02 cell were measured by ultraperformance liquid chromatography-quadrupole time of flight/mass spectrometry(UPLC-QTOF/MS). Result: Genkwa Flos extract exhibited inhibitive effect on L02 cell in a dose-dependent manner. IC50 value was (48.34±4.66) mg·L-1 after 48 hours incubation with L02 cell. Four flavonoids

such as apigenin

3'-hydroxygenkwanin

genkwanin

and velutin

were detected in Genkwa Flos extract. Nine diterpene orthoesters were also detected in Genkwa Flos extract

including yuanhuapine

genkwanine L

ynanhuafine

genkwadaphnin

yuanhuatin

yuanhuagine

yuanhuadine

yuanhuajine

and yuanhuacine. The substances in Genkwa Flos extract that had affinity with L02 were 3'-hydroxygenkwanin

genkwanin

velutin

yuanhuapine

genkwadaphnin

yuanhuatin

yuanhuadine

and yuanhuacine. Among these components

yuanhuacine inhibited the L02 proliferation in a dose-dependent manner with the IC50 of (29.57±2.01) mg·L-1 after 48 hours

while genkwanin(0.1-100 mg·L-1) had no markedly toxic activity on L02. Conclusion: Genkwa Flos extract can inhibit the growth of human liver cell line L02 in vitro. Diterpene orthoesters exhibit cellular affinity with L02 cell and show cytotoxicity

indicating that Diterpene orthoesters are the main substances contributing to the toxicity of Genkwa Flos.