Abstract: Objective To evaluate the relationship of neutrophil-lymphocyte ratio (NLR) and Mayo endoscopic score in ulcerative colitis (UC). Methods Ninety-eight patients with UC and 59 patients with irritable bowel syndrome (IBS) were compared for the differences of NLR between the two groups and in different stages of UC.The ROC curve was used to evaluate the optimal cutoff value of NLR and the area under curve (AUC).Furthermore,we compared the diagnostic efficiency of NLR and C-reactive protein (CRP) in predicting endoscopic activity in UC. Results The NLR value in UC group was significantly higher than that in IBS (2.689 vs.1.865,P<0.001),and the active stage is higher than the healing stage (3.375 vs.1.867,P<0.001).The optimal cutoff value of NLR is 2.473 with 71.0% sensitivity and 75.9% specificity along with a 0.84 AUC.When Mayo ≥ 2,there are 81% patients whose NLR>2.473 while 67% of CRP is positive (P>0.05). Conclusion The difference of NLR value in active and healing stage of UC has statistical significance,positively correlated with CRP.NLR works better than CRP in predicting endoscopic activity in UC.NLR can serve as an objective,convenient,economic indicators to monitor endoscopic activity as well as one of key indexes in colonoscopy screening.