Objective To explore the optimal ratio of Baitong decoction based on efficacy,clarify its spectrum-effect relationship,and identify its potential quality markers.Methods An ulcerative colitis(UC)model in mice was established using dextran sulfate sodium.The efficacy of Baitong decoction with varying drug ratios was assessed by evaluating the apparent score,pathological score and inflammatory factor changes of UC in each group of experimental animals.The fingerprints of Baitong decoction with different ratios were established by high performance liquid chromatography(HPLC),and the relationship between the content of each substance and its efficacy was analyzed by partial least squares regression to determine the potential quality markers of Baitong decoction.Results Baitong decoction was most effective in relieving ulcerative colitis when the mass ratio of Fuzi,Ganjiang and Congbai was 1∶2∶2.The fingerprinting identified 14 common peaks across 7 ratios,with 9 peaks were found to be associated with the remission of ulcerative colitis by partial least squares regression analysis.Conclusion The optimal ratio of Fuzi,Ganjiang and Congbai for treating UC is 1∶2∶2.The spectrum-effect relationship analysis suggested that the quality markers of Baitong decoction may be the substances represented by peak 2(benzoylaconine),3,5,6,8(mesaconine),9(aconitine),10(hypaconitine),13(10-gingerol)and 14.