Asthma manifests as TH2-dominant airway inflammation regulated by inducible T-cell kinase (ITK). To investigate associations between genetic variants of the ITK gene and asthma, 31 single-nucleotide polymorphisms (SNPs) were genotyped in 303 normal controls and 498 asthmatics and the two groups were compared using logistic regression models. The functional effects of the ITK promoter SNP were assessed using pGL3 luciferase reporter systems and gel-shift assays. The minor allele−196C>T in the promoter region of the ITK gene was significantly more frequent in asthmatics than in controls. The luciferase activity of the PGL3-ITK-196T allele construct was higher than that of the −196C allele. In the gel-shift assay, −196T double-stranded oligonucleotides bound more strongly to Jurkat cell nuclear protein compared to the −196C double-stranded oligonucleotides. People with the −rare allele 196C>T may be more susceptible to asthma via transcriptional regulation of the ITK gene.