Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine that triggers dendritic cell-mediated T helper (Th)2 inflammatory responses, and is implicated in the pathogenesis of allergic diseases in humans. Two TSLP splice variants have been reported. To find functional genetic variants that might contribute to disease, we conducted analyses of single nucleotide polymorphisms (SNPs) of the TSLP gene in human bronchial epithelial cells. We surveyed SNPs on the TSLP gene by sequencing genomic DNA from 36 subjects, and characterized the linkage disequilibrium of the gene. We examined whether the SNPs have functional effects on mRNA expression or protein production using real-time PCR, reporter gene analysis, and enzyme-linked immunosorbent assay. We identified a total of 23 polymorphisms in the TSLP gene. The long form of TSLP, which is associated with allergic inflammation, was highly induced by poly(I:C) (double-stranded RNA) stimulation in normal human bronchial epithelial cells (NHBE) (P = 0.0060). The SNP rs3806933 (-847C > T) in the promoter region of long-form TSLP was found to create a binding site for the transcription factor activating protein (AP)-1, and in vitro functional analyses demonstrated that the SNP enhanced AP-1 binding to the regulatory element. The functional variant increased promoter-reporter activity of long-form TSLP in response to poly(I:C) stimulation in NHBE. Functional genetic polymorphism of the TSLP gene appears to contribute to Th2-polarized immunity through higher TSLP production by bronchial epithelial cells in response to viral respiratory infections.