Breast cancer is a disease in which abnormal cells in the breast grow uncontrollably and form a tumor. It is one of the most common cancers worldwide, especially among women, but it can also occur in men. Plant materials have played an important role in cancer treatment—but usually after scientists isolate and refine specific compounds into safe, standardized medicines. The current work aims to assess the intracellular ROS production and apoptosis induction by Alstonia scholaris Linn (A. scholaris) leaf extract in breast cancer cell lines. Column chromatography was used to purify bioactive components from an A. scholaris Linn methanolic extract. Fraction with a significant concentration of phytochemicals was utilized for further investigation. The results of DCFH-DA staining revealed a substantial rise in intracellular ROS levels in A. scholaris Linn-treated cell lines. The dual staining technique (AO/EtBr) was used to examine apoptotic changes. Treatment with A. scholaris Linn substantially enhanced the rate of apoptosis in breast cancer cell lines.