Coronavirus disease 2019 (COVID-19) is an infectious disease, and the reason behind the currently ongoing pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Angiotensin-converting enzyme (ACE2) has been recognized as the specific receptor of the SARS-CoV-2 virus. Although the possible effect of ACE2 gene polymorphism remains unknown, human ACE2 receptor expression influences SARS-CoV-2 susceptibility and COVID-19 disease outcome. In this study, we aimed to investigate the relationship between ACE gene I/D polymorphism, ACE2 receptor gene polymorphism, and COVID-19 severity. ACE gene insertion/deletion (I/D) polymorphism and ACE2 receptor gene rs2106809 and rs2285666 polymorphisms were determined using polymerase chain reaction (PCR) and PCR-based restriction fragment length polymorphism methods, respectively, in 155 COVID-19 patients who were divided into three groups (mild, moderate, and severe) according to clinical symptoms. However, the distribution of genotype and allele frequencies of ACE gene I/D, ACE2 receptor gene rs2106809, and rs2285666 polymorphisms were not statistically significant in all groups. In conclusion, in the study population, ACE gene I/D, ACE2 receptor gene rs2106809, and rs2285666 polymorphisms were not associated with the severity of COVID-19 infection. Although ACE2 receptor gene expression may affect the susceptibility to COVID-19, there is no existing evidence that the ACE or ACE2 gene polymorphisms are directly associated with COVID-19 severity. Interindividual differences in COVID-19 severity might be related to epigenetic mechanisms of ACE2 receptor gene expression or variations in other genes suggested to play a critical role in COVID-19 pathogenesis such as pro-inflammatory cytokines and coagulation indicators.