Background The single-nucleotide polymorphism (SNP) rs11191548, near the CYP17A1 gene, has been identified as being associated with hypertension and systolic blood pressure (SBP) in genome-wide association studies (GWAS) in a European population. The CYP17A1 gene encodes cytochrome P450c17alpha and plays an important role in the steroidogenic pathway, which includes mineralocorticoids. Methods We investigated the SNP rs11191548 in a case-control study of 1,102 subjects with essential hypertension (EH) and 1,109 normotensive controls. Results The SNP rs11191548 was significantly associated with hypertension in an additive genetic model (genotypes CC vs. TC vs. TT; odds ratio (OR) = 1.27 (95% CI, 1.10-1.47; P = 0.001)). The ORs of the TC vs. TT and CC vs. TT genotypes were 1.34 (95% CI, 1.10-1.63; P = 0.003) and 1.52 (95% CI, 1.10-2.12; P = 0.014), respectively. The risk C-allele was associated with increased SBP (βadj ± SEM = 1.307±0.515; P = 0.011) levels in the controls and decreased plasma renin activity (PRA) (βadj ± SEM = -0.053±0.016; P = 0.001) in the subjects with EH. In a stratified analysis of renin-angiotensin-aldosterone-system (RAAS)-related antagonists, the C-allele was significantly associated with decreased serum potassium (K(+)) (βadj ± SEM = -0.093±0.028; P = 0.001) and PRA (βadj ± SEM = -0.067±0.023; P = 0.003) levels in patients with EH who were not taking RAAS-related antagonists. These results remained statistically significant after correction for multiple corrections. Conclusions The SNP rs11191548, near the CYP17A1 gene, was associated with hypertension and SBP in a Chinese Han population. The rs11191548 polymorphism was also related to lower PRA and K(+) levels, suggesting that it has an effect on the enzymatic activity of CYP17A1.