Abstract: AIM: To investigate the genetic polymorphism of cytochrome P450 (CYP) 2C9 and angiotension I-converting enzyme genes (ACE) in Chinese Han patients with essential hypertension (EH) in Guangdong Province. METHODS: Polymerase chain reaction (PCR) and gene sequence detection were used to detect CYP2C9 and ACE genotypes in 206 EH cases in Guangdong Chinese Han patients. RESULTS: In the 206 EH patients, frequency distribution of 1 075 C for CYP2C9*3 was 3.2%, and no significant difference was observed in the allelic frequencies of CYP2C9*3 between Guangdong Chinese Han patients with EH and Guangdong population. Allelic frequencies of D and I in ACE gene were 56.3% and 43.7%, respectively, and D allelic frequency in ACE gene in Guangdong Chinese Han patients with EH was significantly higher than in healthy populations in Guangdong and other areas in China (P<0.05). CONCLUSIONS: In Chinese Han patients with EH in Guangdong, we did not find that the CYP2C9*3 allele was associated with EH. Otherwise, D allele of the ACE gene is likely in association with EH. Detecting the genotypes of CYP2C9 gene and ACE gene in EH patients may be helpful to individual clinical antihypertensive therapy.