There is an urgent need to improve the clinical management of hepatocellular carcinoma (HCC), one of the most common causes of global cancer-related deaths. Zingibar officinale is a medicinal herb used throughout history for both culinary and medicinal purposes. It has antioxidant, anticarcinogenic, and free radical scavenging properties. Previously, we proved that the crude flavonoid extract of Z. officinale (CFEZO) inhibited growth and induced apoptosis in several cancer cell lines. However, the effect of the CFEZO on an HCC cell line has not yet been evaluated. In this study, we explored the anticancer activity of CFEZO against an HCC cell line, HepG2. CFEZO significantly inhibited proliferation and induced apoptosis in HepG2 cells. Typical apoptotic morphological and biochemical changes, including cell shrinkage and detachment, nuclear condensation and fragmentation, DNA degradation, and comet tail formation, were observed after treatments with CFEZO. The apoptogenic activity of CFEZO involved induction of ROS, depletion of GSH, disruption of the mitochondrial membrane potential, activation of caspase 3/9, and an increase in the Bax/Bcl-2 ratio. CFEZO treatments induced upregulation of p53 and p21 expression and downregulation of cyclin D1 and cyclin-dependent kinase-4 expression, which were accompanied by G2/M phase arrest. These findings suggest that CFEZO provides a useful foundation for studying and developing novel chemotherapeutic agents for the treatment of HCC.