Thymic stromal lymphopoietin (TSLP) is a cytokine similar to IL-7, which is released by airway epithelial cells in response to injury and inflammation. Current literature is contradictory about the association between different single nucleotide polymorphisms (SNPs) of the TSLP gene and asthma development in different countries. We aimed to evaluate the association between two common TSLP SNPs (rs2289276 and rs2289278) and the risk of asthma in the Iranian population. Genotyping of the TSLP gene was performed in 126 adult asthmatic patients and 300 controls; using the TaqMan genotyping assay. Moreover, total serum IgE level and eosinophil count were assessed. The results indicated that the TT genotype of rs2289276 was inversely associated with the risk of asthma (p=0.002). A similar inverse association was detected in subgroups of atopic (p=0.001) and non-atopic (p=0.005) asthma. Moreover, the TT genotype of this SNP was more prevalent in severe and late-onset categories of asthma. In subgroup analysis, a significant sex-specific association between rs2290276 and asthma was observed in women (p=0.004). The prevalence of rs2289276 was extremely low, which made it infeasible to perform any further analysis. Overall, our findings indicated that rs2290276 SNP of the TSLP gene has a protective phenotype against asthma development in the Iranian population.