Uterine leiomyomas, or fibroids, are common benign tumors that affect a significant percentage of women, with treatment options ranging from medication to surgery. Carbobenzoxyl-L-leucyl-L-leucyl-L-leucine (MG132), a proteasome inhibitor, has exhibited potential in treating various cancers by disrupting key cellular processes such as apoptosis and cell cycle regulation. The present study aimed to evaluate the effects of MG132 on the viability, proliferation, apoptosis, and the production of reactive oxygen species (ROS) in Eker leiomyoma tumor-3 (ELT3) uterine leiomyoma cells and to elucidate the underlying molecular mechanisms involved. Cell viability was evaluated using an MTT assay, while cytotoxicity was assessed using a lactate dehydrogenase (LDH) release assay. Colony formation assays assessed the long-term effects of MG132. Apoptosis and cell cycle distribution were analyzed using flow cytometry with Annexin V staining, and ROS production was also measured by flow cytometry. Western blot analysis was performed to examine key proteins related to the cell cycle and apoptosis. The findings of the present study revealed that MG132 significantly reduced the cell viability and impaired colony formation in ELT3 cells, as evidenced by decreased cell viability and increased LDH activity. MG132 treatment significantly increased apoptosis and induced cell cycle arrest at the G2/M phase. Additionally, MG132 increased the levels of ROS, which contributed to ROS-mediated apoptosis. Western blot analysis revealed that MG132 modulated key proteins involved in cell proliferation and apoptosis, including p21, p27, ERK, and caspase-3. Furthermore, MG132 treatment induced autophagy, as indicated by the increased conversion of LC3 I to LC3 II. Overall, MG132 was revealed to exert potent cytotoxic effects on ELT3 uterine leiomyoma cells by inducing ROS-mediated apoptosis and cell cycle arrest, and triggering autophagy. These findings suggest that MG132 provides a proof of concept for targeting the proteasome in uterine leiomyomas.