The inverse association between plasma B-type natriuretic peptide (BNP) levels and body mass index (BMI) has been reported in Western populations. Here we analyzed the relationship between plasma BNP and obesity in a general urban Japanese population. We recruited 1,759 subjects without atrial fibrillation or history of ischemic heart disease aged 38-95 years (mean age ± standard deviation 64.5 ± 10.9 years, 56.1% women, mean BMI 22.8 ± 3.1 kg/m²) from the participants in the Suita Study between August 2002 and December 2003. In multivariable regression analyses adjusted for age, systolic blood pressure, pulse rate, serum creatinine, left ventricular hypertrophy in ECG, the inverse relationships between BNP levels and BMI (kg/m²) was found in both sexes (both p<0.001). Multivariable-adjusted mean plasma BNP levels in the group of BMI<18.5, 18.5≤BMI< 22, 22≤BMI<25, and 25≤BMI were 23.4, 17.9, 14.0 and 13.0 pg/mL, respectively (trend p<0.001). The negative association of body fat (percentage and mass), skin fold thickness, or waist circumference with BNP levels was observed the negative associations in both sexes (p<0.01). Among the obesity indices, body fat mass is most tightly associated with BNP. In conclusion, plasma BNP was inversely associated with obesityrelated markers such as body fat mass, skinfold thickness and waist circumferences after adjusted for relevant covariates in a Japanese population.