Aims: This study aimed to investigate the cytotoxic and apoptotic effects of Prunus mahaleb (P. mahaleb) ethanolic extract (MEE) on the PC3 human prostate cancer cell line and the PNT1A cell line.Methods: MEE was prepared from P. mahaleb fruit using ethanol extraction followed by lyophilization. Cell viability was assessed using the WST-8 assay at concentrations of 2500, 3000, and 3500 μg/ml at 24, 48, and 72 hours, with cell-free blank correction applied at each concentration to account for the intrinsic absorbance of the extract. The expression of apoptosis related proteins-Caspase-3, Caspase-8, Caspase-9, and BAX-was evaluated by immunofluorescence staining. Morphological changes were monitored by differential interference contrast (DIC) optical microscopy at 48 hours. Statistical analyses were performed using one-way ANOVA with Tukey HSD post-hoc test (p