The human genome contains sequences derived from endogenous retroviruses (HERVs), which constitute approximately 8% of chromosomal DNA. Most HERVs are currently inactive and noninfectious due to recombination, deletion, and mutation after integration into the host genome. However, recent studies have implicated HERVs as mutagens of intracellular genes, contributing to autoimmune diseases and tumors. Several studies have shown a significant association between HERVs and certain cancers. We focused on knocking out the HERV-R (ERV3-1) env gene in the DLD1 colon cancer cell line. A 208-bp deletion was confirmed by genomic PCR and DNA sequencing. As a result, HERV-R env gene expression was significantly lower in DLD1 HERV-R knockout (HERV-R KO) cells compared to control cells at both RNA and protein levels. Additionally, the invasion and migration abilities of HERV-R KO cells were significantly reduced. In vivo experiments on mice injected with HERV-R KO cells showed smaller tumor sizes compared to mice injected with control cells, suggesting that HERV-R env plays an important role in tumor growth. Further mRNA-seq analysis identified genes associated with cell invasion and migration. The STRING tool, which analyzes gene correlations, confirmed that HERV-R is linked to genes involved in cancer proliferation, migration, and invasion in colon cancer. This study suggests that the expression of the HERV-R env gene influences the tumorigenic properties of colon cancer, providing valuable evidence for potential clinical studies in colon cancer patients.