BACKGROUND: nitric oxide (NO) plays a role in almost every biologic system including regulation of energy balance and food intake. This study aimed at determining association between serum nitric oxide metabolite (NOx) levels and obesity in a population-based study.METHODS: In a cross-sectional study, NOx levels were measured in 3505 adult participants. Pregnant women and those with diabetes, renal dysfunction, chronic diarrhea, and hospitalization within the past three months, subjects using antihypertensive medications or aspirin, and those with missing data were excluded. Finally, 2445 subjects (1004 men and 1441 women) were included.RESULTS: Women with body mass index (BMI)>30 kg/m2 compared to those with BMI<25 kg/m2, had significantly higher serum NOx concentrations after multivariable adjustment (B=5.24, P=0.002). In addition, there was a significant trend of increasing serum NOx concentrations in categories of BMI in women. Women with a waist circumference (WC)≥90 cm had significantly higher serum NOx concentration even after multivariate adjustment. Women with waist-to-hip ratio (WHR)≥0.90 had significantly higher serum NOx concentration; however, the association was not significant after multivariable adjustment. None of the parameters were significantly associated with NOx in men.CONCLUSION: A positive association between BMI and WC and serum NOx concentration was found in women which might be a reflection of increased NO production.