Apoptosis induction in tumor cells is a fundamental therapeutic approach in cancer treatment, with growing interest in plant-derived compounds that offer potent efficacy and reduced toxicity. Cephalotaxus harringtonia, traditionally used in East Asian medicine, contains several bioactive constituents, including homoharringtonine (HHT) and quercetin 3-β-D-glucoside (Q3G), which are known for their anticancer properties. This study investigated the anticancer effects of C. harringtonia leaf extract (CHLE) and its two major compounds, quercetin 3-β-D-glucoside (Q3G) and HHT, against human liver cancer cell lines (HepG2). CHLE exhibited selective cytotoxicity and apoptosis specifically in HepG2 cells while showing minimal toxicity toward normal kidney cells (HK-2). Mechanistic analyses revealed that CHLE induced apoptosis through a mitochondria-mediated intrinsic pathway, characterized by increased reactive oxygen species production, mitochondrial membrane depolarization, and BAX upregulation. These findings demonstrate that C. harringtonia leaf extract possesses potent, selective anticancer activity and may serve as a promising natural candidate for the prevention and therapeutic management of liver cancer.