Objective: To explore the dose-effect relationship and‘dose threshold’parameter of Gegen Qinlian decoction in treating the picrylsulfonic acid solution (TNBS) indeced-ulcerative colitis rats. Method: The experimental ulcerative colitis model induced by TNBS/ethanol

except for the normal group

then divided into model group

sulfasalazine group

and Gegen Qinlian decoction 1.65

4.95

8.25

11.55

14.85

18.15

21.45

24.75

28.05 g·kg-1

administered once a day for 5 days.then measured and calculated the disease activity index (DAI) index

and detected the myeloperoxidase(MPO)

malondialdehyde(MDA)

superoxide dismutase(SOD levels in tissue homogenate.Through used the GraphPad Prism 6 software to establish the dose-response and calculate the dose-related parameters. Result: By the comprehensive analysis of experimental data

the dose-effect relationship of MPO appeared the‘S’shape

and the dose threshold parameters are as follows:D20-D80 15.39-17.11 g·kg-1

median dose:D50 16.25 g·kg-1

the threshold dose:D20 15.39 g·kg-1. Conclusion: Gegen Qinlian decoction showed dose-response curves as‘S’shape in treatment of ulcerative colitis rats

suggesting a dose-dependent range is between 15.39 g·kg-1 to 17.11 g·kg-1.