Heme oxygenase-1 (HO-1) which is a rate-limiting enzyme in heme degradation processes shows a dinucleotide GT repeat in the promoter that alters the level of gene transcription. This study is aimed to assess the association of HO-1 gene promoter polymorphism and metabolic syndrome (MetS). A hundred and fifty two individuals, who were followed in Isfahan Cohort Study since 2001, were enrolled in this study. They consisted of 78 MetS patients and 74 controls without MetS. Blood samples were obtained from all participants and after extracting the genomic DNA, promoter sequence was determined by PCR-based genotyping. The serum levels of iron, ferritin and bilirubin were also measured in all subjects. The proportion of short and long allele frequency did not significantly differ in patients with metabolic syndrome compared to control group. In conclusion, the results showed that there is no significant difference between two groups in (GT)n repeat of HO-1 gene promoter. These findings suggest the insignificant role of genetic risk factors compared to environmental risk factors in the development of MetS.