This study was aimed to determine whether the leptin receptor Gln223Arg polymorphism has an effect on plasma leptin levels and left ventricular hypertrophy in hypertension. The genotypes and allelic frequencies of the leptin receptor Gln223Arg were examined using the polymerase chain reaction and restriction fragment length polymorphism in 190 hypertensive patients and 88 healthy controls. Logarithmic (log) transformation of the plasma leptin level was carried out before performing comparison and regression analysis. The values of log(plasma leptin levels) in the hypertensive patients were higher than those of controls and they were higher in hypertensive patients with left ventricular hypertrophy than those without it (P < 0.05). The genotype (AA, AG, and GG) distribution of Gln223Arg polymorphism was 6.8, 33.8, and 59.4% in hypertensive patients with left ventricular hypertrophy, 4.3, 27.6, and 68.1% in patients without left ventricular hypertrophy, and 2.3, 26.1, and 71.6% in the controls, respectively. A significant difference was found among these three groups (P < 0.05). The frequency of allele A was higher in patients with left ventricular hypertrophy than in patients without it (23.6 vs. 18.1%; P < 0.05). Log(plasma leptin levels) and left ventricular mass index were higher in patients with the AA genotype than those with the AG or GG genotype in hypertensive patients (P < 0.05). In multivariate regression analysis, the AA genotype as an independent predictor had statistically significant effects on the left ventricular mass index. Our results suggest that the Gln223Arg polymorphism of the leptin receptor is significantly associated with plasma leptin levels and left ventricular hypertrophy in hypertension.