Objective To explore the diagnostic value of prothrombin time(PT),activated partial thromboplastin time(APTT),fibrinogen(FIB),D-Dimer(DD),antithrombin Ⅲ(ATⅢ),platelet(PLT)in activity and severity assessment of ulcerative colitis(UC),and to analyze whether they could evaluate the degree of activity UC in children.Methods The data of UC patients in the Department of Gastroenterology,Children's Hospital of Nanjing Medical University from January 2012 to September 2016 were analyzed,25 cases of remission and 36 cases of active UC patients were selected as the study subjects.Thirty healthy children were selected as healthy control group,combined with the coagulation function indicators for analysis.Results Receiver operating characteristic area under the curve(AUC)of PT,APTT,FIB,DD,ATⅢ and PLT in UC patients was 0.659,0.840,0.744,0.776,0.599 and 0.792,the activity of UC patients was 0.849,0.889,0.836,0.912,0.964 and 0.966,respectively.The results of PT,APTT,FIB,DD and PLT in children with active UC were significantly higher than those in the healthy control group,and ATⅢ was significantly lower than that in the healthy control group.Compared with the healthy controls,the levels in remission UC patients were not significantly different(P>0.05).The 3 subgroups of activity UC had no significant differences among PT and APTT(F=0.652,1.755,all P>0.05),However,there were significant differences among FIB,DD,ATⅢ and PLT(F=66.495,32.817,88.284,22.892,all P<0.05).FIB,DD and PLT were moderately positively correlated with severity of activity UC patients(r=0.857,0.648,0.654,all P<0.05),and ATⅢ had moderately negative correlation(r=-0.789,P<0.05).Progressive regression analysis showed that the severity of UC was associated with FIB,DD and ATⅢ(R2=0.830,F=39.962,P<0.05).Conclusion FIB,DD and ATⅢ can be used as index for the activity and evaluation of UC.