Objective To explore the relationship between serum leptin and renin-angiotensin-aldosterone system (RAAS) with essential hypertension, as well as pathophysiological mechanisms. Methods The serum leptin, plasma rennin activity (PRA), angiotensinⅡ(AngⅡ) and aldosterone (ALD) wwere measured by radioimmunoassay in 91 patients with essential hypertension and 67 healthy volunteers. Their body height and weight were measured, and the body mass index (BMI) was calculated. Results The serum leptin concentration was significantly higher in female than in male among the same group (P<0.01)．The leptin levels in hypertension women patient group were significantly higher than those of the normal women group (P<0.01). The leptin levels of hypertension men patient group were also significantly higher than those of the normal men group (P<0.05). The leptin levels, PRA, systolic blood pressure (SBP) and diastolic blood pressure (DBP) in patient of primary hypertension were significantly higher than those in the control group (P<0.01). Serum concentrations of AngⅡ were also much higher than those in healthy volunteers (P<0.05). Two groups did not differ in BMI and ALD. The correlation analysis showed that the serum leptin in patients of primary hypertension group was positively correlated with PRA, AngⅡ, BMI and SBP (PRA:r=0.52, P<0.01; AngⅡ: r=0.43, P<0.01; BMI: r=0.55, P<0.01; SBP:r=0.33, P<0.05), but not with ALD and DBP. The leptin in the control group was only positively correlated with BMI(r=0.54 P<0.01), but not with others. Conclusion The effect of serum leptin levels on blood pressure is related with gender. Leptin resistance exists in patients with primary hypertension. Leptin could cause an increase of blood pressure，especially SBP，in primary hypertension patients by regulating the activeness of RAAS.