The usefulness of urinary hydrogen peroxide (H(2)O(2)) as an oxidative stress biomarker was evaluated in 766 healthy Japanese. The mean level of urinary concentrations of H(2)O(2) was 5.66 ± 8.27 μmol/g creatinine, and was significantly higher in females than in males. Significant correlations of H(2)O(2) were observed with age, aspartate aminotransferase (AST), alanine aminotransferase (ALT), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), insulin, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and exercise habit in females. In both sexes, H(2)O(2) showed a significant correlation with 8-OHdG. By a multiple logistic regression analysis, urinary H(2)O(2) was positively associated with urinary 8-OHdG and TC and was inversely associated with insulin. By stratification of sex and age, the association of urinary H(2)O(2) with TC was positive in both sexes under 50 years old and was inverse in males over 50 years old, and that with insulin was inverse in males over 50 years old and in females under 50 years old. Moreover, by stratification of sex and age, a positive association of H(2)O(2) with exercise and an inverse association of H(2)O(2) with alcohol consumption became clear in males under 50 years old, although there were no significant odds for H(2)O(2) after adjustment for covariates. In conclusion, the present results suggest that urinary H(2)O(2) is a useful biomarker for oxidative stress, showing an association with 8-OHdG, TC, and insulin independently.