Oncolytic virotherapy (OV) is the use of viruses that do not target normal human cells to infect and destroy cancer cells; some also stimulate the immune system against the tumors. Myxoma virus (VMYX) is a candidate for use as an oncolytic agent, as it is not pathogenic to humans and can infect a variety of human cancer cells. VMYX also can initiate immune responses against the virus-infected tumor. Thus, we investigated the oncolytic efficacy of a few recombinant constructs of VMYX on triple-negative breast cancer (TNBC), a highly aggressive subtype of breast cancer with limited treatment options. TNBC lacks an estrogen receptor, progesterone receptor, and HER2, which render hormone-based therapies useless. Further challenges of TNBC include early metastasis and recurrence, as well as poor prognosis due to a lack of molecular targets. Here, we utilized 4T1-Luc2 cells, an in vitro mouse model of TNBC, to examine the oncolytic potential of recombinant viral constructs of VMYX. Ability to infect was measured by fluorescence intensity, while ability to induce cytotoxicity was measured through MTS and SYTOX assays. Further characterization of cell death was performed using Caspase 3/7 activity assay, immunofluorescent staining and confocal microscopy to detect ecto-expression of calreticulin, and ATP release assays. We demonstrated the ability of recombinant VMYX constructs to infect and induce cell death in 4T1-Luc2 cells. VMYX-p14-FAST-GFP induced the most cell death, while VMYX-M011LKO-GFP best activated Caspase 3/7. Through ATP release assays and examination of ecto-expression of calreticulin, preliminary data indicated that VYX-135KO-GFP is unable to stimulate immunogenic cell death, a form of cell death that stimulates an adaptive immune response, in these cells. Future directions include further characterization of cell death in vitro, as well as in vivo studies.