The innovation of therapeutic modalities with better clinical efficacy is necessary for the treatment of patients with advanced cancers. Newcastle disease virus (NDV), an avian pathogenic virus, is one of the most promising oncolytic viruses that can replicate selectively in human cancer cells. In humans, NDV can cause transient conjunctivitis and mild flu-like symptoms. However, this virus poses no hazard to human health. The elucidation of the mechanisms of cancer cell killing by NDV is helpful for the clinical application of NDV in cancer patients. Regarding this, the present study was performed to evaluate apoptosis induction by NDV LaSota strain vaccine in human breast carcinoma cells. To this end, MCF-7 cells, a human breast adenocarcinoma cell line, were infected with NDV in vitro. Tumor cell cytotoxicity, apoptosis induction, and expression levels of apoptosis-related genes were examined in NDV-infected breast carcinoma cells. Tumor cell cytotoxicity was measured by 3-[4,5-dimethylthiazol-2yl]2,5-diphenyl-tetrazoliumbromide (MTT) assay. The induction of apoptosis was assessed by annexin V/propidium iodide staining. In addition, the expression levels of apoptosis-related genes were evaluated using real-time reverse transcription polymerase chain reaction (PCR) technique. The NDV showed cytotoxic effects on MCF-7 cells and induced apoptosis in the infected carcinoma cells. The gene expression levels of BAX, caspase-9, and caspase-3, but not BAK-1, were increased in NDV-infected cancer cells, compared to the gene expression levels in the non-infected cancer cells. These results suggest that the induction of the intrinsic pathway of apoptosis is one of the mechanisms that can contribute to cancer cell killing by NDV. Additional studies are required to investigate other probable mechanisms involved in NDV-mediated cancer cell killing.