Apoptosis, a form of programmed cell death, is a critical defense mechanism against the formation and progression of cancer. In vivo, apoptosis functions to eliminate potentially deleterious cells without causing such adverse effects as inflammatory response, and to ensue scar formation. Therefore, activation of the apoptotic pathways becomes an intriguing strategy in the development of chemotherapeutic agents. Marine natural products have become an important source in the discovery of antitumor drugs now since it is more and more feasible to collect organisms from seas. Hundreds of marine compounds have been found to induce apoptosis in tumor cells in recent years and many of them have good antitumor activity. This review summarizes several such compounds, based on their effects on the apoptotic signaling pathways, and highlights the problems in the development of anti-cancer drugs from the natural products.