Although (GT) (n) repeats in heme oxygenase-1 (HO-1) promoter may modulate gene transcriptional activity, the association between (GT) (n) repeats polymorphism and risk of coronary heart disease (CHD) from different levels of oxidative stress (OS) is unknown. We determined the allelic frequencies of (GT) (n) repeats in the HO-1 gene promoter and plasma malonaldehyde (MDA) as biomarkers of OS in 2,298 pairs of CHD patients and controls in the Chinese population. Furthermore, we measured MDA in culture mediums and HO-1 expressions levels in cell lysates of endothelial cells carrying various (GT) (n) genotypes under different concentrations of H2O2. Compared with L/L genotype (> 25 repeats) carriers, the adjusted odd ratios for S/S genotype (a parts per thousand currency sign25 repeats) in subjects with different levels of OS (MDA < 1.83, 1.83-2.91, > 2.91 mu mol/L) were 1.06 (95%CI, 0.75 to 1.49), 0.79 (95%CI, 0.55 to 1.12), and 0.60 (95%CI, 0.44 to 0.81), respectively (P (interaction) = 0.002). In biological experiments, compared with endothelial cells carrying L/L genotype, cells with S/S genotype did not have a significantly higher HO-1 expression under 0 mu mol/L H2O2, but displayed a significantly higher HO-1 expression under 50 mu mol/L H2O2 (P (interaction) = 0.003). S/S genotype in HO-1 gene promoter is associated with a lower risk of CHD in subjects with higher levels of OS, because under conditions of high OS, the S/S genotype has higher levels of HO-1, an antioxidant.