Abstract: Objective To detect the interleukin 33 level in elderly acute coronary syndromes(ACS) complicated with diabetic mellitus (DM) and to explore the relationship between IL-33 level and ACS with DM in elderly patients. Methods A total of 188 patients(age ≥ 65 years) with coronary angiography in our hospital were summarized including 105 males,averaged (70.8±4.4)years old.The patients were divided into 3 subgroups:Control group(n=64 normal subjects),ACS without DM group(n=73) and ACS+DM group(n=51).Plasma IL-33 levels were measured by ELISA and the vascular stenosis degree was quantitatively calculated with Gensini score. Results The IL-33 levels in ACS+DM group were significantly higher than those in ACS without DM group(P<0.01),and the IL-33 levels in ACS without DM group were significantly higher than those in the control group(P<0.01).Compared with ACS without DM group,the ACS+DM group had more patients with multiple vascular lesions and less patients with single vascular lesions(P<0.01).The Gensini score was positively related to IL-33 level in both ACS+DM group and ACS without DM group(r=0.663,P<0.01). Conclusion The plasma IL-33 level is high in elder ACS patients and the elevation level is related to vascular lesion degree complicated with DM,which indicate that the inflammatory reaction mat be present in vascular endothelial with those patients.