Human cytochrome P450 4A11 (CYP4A11) plays a role in the regulation of blood pressure through the conversion of arachidonic acid into 20-hydroxyeicosatetraenoic acid (20-HETE). We therefore investigated the association between a CYP4A11 polymorphism (rs9333025) with hypertension in the Mongolian and Han ethnic groups. We studied 514 Mongolians in a pastoral area, including 201 hypertension patients and 313 normotensive controls, and 524 Han individuals in an urban area, including 215 hypertension patients and 309 normotensive controls. Genotyping was performed using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). Genotype, allele, and dominant inheritance differed significantly between the Mongolian and Han populations (P = 0.006, P = 0.002, and P = 0.003, respectively). Significant differences were also observed in these factors when considering only males (P = 0.001, P = 0.003, and P = 0.001, respectively). For the Han population, recessive inheritance differed significantly between hypertension patients and controls and between male patients and controls (P = 0.005 and P = 0.049, respectively). The genotypic, allelic, and dominant frequencies differed significantly between hypertension patients in both populations (P = 0.019, P = 0.035, and P = 0.024, respectively). The genotypic frequency in Mongolian male patients was significantly different from that in Han male patients (P = 0.009). Higher body mass index, triglycerides, and lower high-density lipoprotein were associated with increased risk of developing hypertension in the Han population. The GG genotype was in higher frequency in the Mongolian population, indicating that it is a high risk factor for hypertension. Mongolian men were at higher risk of developing hypertension.