Psoriasis, an inflammatory skin disease, was associated with a promoter variant (rs9267502; P = 3.786 × 10(-19)) of LST1 that may regulate immune response and cellular morphogenesis. Promoter activity was examined to identify functional variants in the proximity of the associated variant. Five natural haplotypes (H1-H5) of four variants (rs7758790, rs9267502, rs41268884, rs17200775) in strong linkage disequilibrium were investigated. The most common haplotype (H1) was TGAG (frequency 0.78), and the second most frequent haplotype (H2) was CGGG (0.09). Luciferase assay was conducted using reporter constructs including each haplotype and firefly luciferase gene. As a result, promoter activity of H1 was smaller than the construct without the promoter region (P < 0.05). The promoter activities of H3, H4, and H5 corresponded to that of H1 (P > 0.05), and H2 promoter activity was larger than that of H1, H3, H4, and H5 (P < 0.05). This might result from changes in binding affinity to transcription factors by nucleotide substitutions of the promoter variants of the LST1 gene.