Cytisine is a quinolizidine alkaloid, which has been reported to be among the major bioactive components of Sophora alopecuraides L. Quinolizidine alkaloids have previously been demonstrated to inhibit the proliferation of several types of tumor cells. However, few studies have investigated the effects of cytisine on cancer cells. The present study was performed to further investigate the molecular mechanisms underlying cytisine‑induced apoptosis of HepG2 human hepatocellular carcinoma cells. The results of an MTT assay demonstrated that cytisine inhibited the growth of HepG2 cells in a dose‑dependent manner. In addition, the induction of apoptosis was detected, as determined by morphological observation and flow cytometry. As determined by fluorescence microscopy, apoptotic morphological alterations were detected following cytisine administration. Flow cytometric analyses demonstrated that cytisine induced cytotoxicity through apoptosis‑like mechanisms in HepG2 cells. Furthermore, western blot analysis was performed to investigate the release of cytochrome c (Cyt‑c) and activation of the caspase cascade, and the results indicated that treatment of HepG2 cells with cytisine induced caspase‑dependent apoptosis via the release of Cyt‑c from the mitochondria, upregulation of caspase‑3 and downregulation of pro‑caspase‑3. These results indicated that cytisine may induce apoptosis of HepG2 cells through the mitochondrial pathway.