Ischemic stroke is a complicated disease, and its pathogenesis has been attributed to the occurrence of genetic polymorphisms. Evidence has suggested that the microRNA let-7a is involved in the pathogenesis of ischemic stroke. Pri-miRNA is the primary transcript, which undergoes several processing steps to generate pre-miRNA and, later, mature miRNAs. In this case-control study, we analyzed the distribution of pri-let-7a-2 variants in patients at a high risk for ischemic stroke and the interactions of pri-let-7a-2 variants and environmental factors. Blood samples and clinical information were collected from 1086 patients with ischemic stroke and 836 healthy controls between December 2013 and December 2015 at the First Affiliated Hospital of China Medical University. We found that the rs1143770 CC genotype and the C allele were associated with a decreased risk of ischemic stroke, whereas the rs629367 CC genotype was associated with an increased risk for ischemic stroke. Moreover, these two single-nucleotide polymorphisms were in linkage disequilibrium in this study sample. We analyzed gene-environment interactions and found that rs1143770 exerted a combined effect on the pathogenesis of ischemic stroke, together with alcohol use, smoking, and a history of hypertension. Therefore, the detection of pri-let-7a-2 polymorphisms may increase the awareness of ischemic stroke risk. This study was approved by the Institutional Ethics Committee of the First Affiliated Hospital of China Medical University, China (approval No. 2012-38-1) on February 20, 2012, and was registered with the Chinese Clinical Trial Registry (registration number:ChiCTR-COC-17013559) on December 27, 2017.