Chronic inflammation has been implicated as one of the important etiological factors in insulin resistance and type 2 diabetes mellitus (T2DM). To investigate the role of anti-inflammatory cytokines in the development of T2DM, we conducted a case-control study to assess the association between IL4/IL4R polymorphisms and disease risk. We firstly identified single nucleotide polymorphisms (SNP) at IL4 and IL4RA loci by sequencing the loci in Korean participants. Case-control studies were conducted by genotyping the SNPs in 474 T2DM cases and 470 non-diabetic controls recruited from community-based cohorts. Replication of the associated signals was performed in 1,216 cases and 1,352 controls. We assessed effect of IL4-IL4RA interaction on T2DM using logistic regression method. The functional relevance of the SNP associated with disease risk was determined using a reporter expression assay. We identified a strong association between the IL4 promoter variant rs2243250 and T2DM risk (OR=0.77; 95% CI, 0.67~0.88; p=1.65x10-4 in the meta-analysis). The reporter gene expression assay demonstrated that the presence of rs2243250 might affect the gene expression level with ~1.5-fold allele difference. Our findings contribute to the identification of IL4 as a T2D susceptibility locus, further supporting the role of anti-inflammatory cytokines in T2DM disease development.