Walsuronoid B is a limonoid compound extracted from Walsura robusta. Previous studies have shown that limonoid compounds possess anti-cancer potential, although the molecular mechanism of this activity remains elusive. In this study, we demonstrated for the first time that walsuronoid B inhibited cell proliferation in several human cancer lines. Liver cancer cells (HepG2 and Bel-7402) were chosen for their high sensitivity to walsuronoid B. Walsuronoid B induced cell death through G2/M phase arrest and apoptosis and induced the accumulation of autophagosomes through the suppression of mTOR signaling, which serves as a cell survival mechanism and prevents cell death. We further examined the molecular mechanisms and found that walsuronoid B-induced dysfunction of the mitochondria and lysosomes rather than the endoplasmic reticulum contributed to its cell death effect. Walsuronoid B enhanced the generation of hydrogen peroxide, nitric oxide and superoxide anion radical, resulting in elevated levels of reactive oxygen species (ROS). In addition, ROS induced by walsuronoid B upregulated p53 levels; conversely, p53 stimulated ROS. These results suggested that ROS and p53 reciprocally promoted each other's production and cooperated to induce liver cancer cell death. We found that the induction of ROS and p53 significantly triggered G2/M phase arrest and mitochondrial and lysosomal apoptosis. Finally, walsuronoid B suppressed tumor growth in vivo with few side effects. In summary, our findings demonstrated that walsuronoid B caused G2/M phase arrest and induced mitochondrial and lysosomal apoptosis through the ROS/p53 signaling pathway in human liver cancer cells in vitro and in vivo.