Background/Objectives: Natural products are important in healthcare due to their accessibility and linkage to a healthy lifestyle. However, their effectiveness is uncertain due to insufficient scientific data. Cancer patients are frequent users of natural products to relieve symptoms or for chemoprevention. Eugenia uniflora leaf essential oil (EO), traditionally used for digestive disorders, emerges as a potential antineoplastic agent. We investigated the cytotoxic and antiproliferative effects of E. uniflora EO in human normal CCD 841 CoN and tumoral Caco-2 colonic cell lines. Methods: CCD 841 CoN and Caco-2 cells were exposed to different concentrations of E. uniflora EO, and the cytotoxicity was determined by MTT and Trypan Blue assays. Cell proliferation kinetics were analyzed at a low EO concentration, and the induction of DNA damage and oxidative stress was assessed by Comet and Cellular ROS assays. Results: Both cell lines exhibited cytotoxicity produced by the EO and decreased cell viability of the exposed cells and their progeny. CCD 841 CoN proliferation was impaired by low EO concentration, while the proliferation kinetics of the Caco-2 cells was modified. EO treatment induced variable DNA damage and oxidative stress depending on the cell line. Conclusions: Our results suggest that E. uniflora EO may prevent the proliferation of normal cells, inducing loss of viability. The EO produced cytotoxic and antiproliferative effects in tumoral cells by inducing DNA damage and increased oxidative stress. These effects support the consideration of E. uniflora EO (or its bioactive compounds) as a potential agent for the chemoprevention and treatment of colorectal cancer.