Aim To explore the relationship between serum leptin and essential hypertension, degree of obesity.Methods Serum leptin concentrations were measured by radioimmunoassay. Systolic blood pressure (SBP), diastolic blood pressure (DBF), body mass index (BMI), body fat percentage and fasting blood glucose (FPG) were determined in 115 patients with grade 1 hypertension (51 males, 64 females), 96 patients with grade 2 hypertension (36 males, 60 females) and 47 normo-tensives (23 males, 24 females). The correlation between leptin and other parameters were analyzed. Results Serum leptin concentrations were strongly correlated with BMI and BF percentage in both male and female ( P< 0.001). The concentration level was significantly lower in normotensives group than in grade 1 hypertension group and in grade 2 hypertension group among same gender. The difference in serum leptin concentrations between the three same gender groups disappeared when body fat percentage was corrected by analysis of covariance. Serum leptin concentrations in male and female separately were significantly correlated with SBP, DBP, age, BMI, body fat percentage and FPG (p<0.05-p<0.001). There was a more highly significant correlation between serum leptin concentrations and SBP, DBF in female than in male, but after adjustment for body fat percentage, partial correlation analysis showed that serum leptin concentrations were not correlated with SBP, DBP in both male and female. Logistic regression analysis revealed that serum leptin concentration was not a significant independent predictor of blood pressure in both male and female. Conclusion Serum leptin concentrations are not directly related to essential hypertension in both male and female, but the concentration levels are actually correlated with body fat percentage.