Leukemia is a hematological neoplasm with abnormal genetic mutation or chromosomal translocation in the myeloblast or lymphoblast, and characterized by accumulation of immature cells and malfunction of lymphocytes and myeloid-derived cells. The prognosis of treatment depends on genetic mutation, chromosomal aberration, disease progression and age of patients. Currently, bone marrow transplantation is a useful therapeutic strategy, but the success in therapy is limited by the bone marrow of donors and life-threatening events such as immune repulsion. Although chemotherapy improves leukemia treatment, long-term chemotherapy usually leads to the production of drug-resistant cancer cells. Thus, the development of new modality in overcoming drug-resistant should be beneficial for in leukemia therapy. In this thesis, Naja nigricollis toxin £^, piceatannol, caffeine, and Bungarus multicinctus protease inhibitor-like protein 1 (PILP-1) are employed to investigate the molecular mechanisms in regulating apoptosis and invasion of leukemic cell lines K562 and U937. Hopefully, the signaling pathways elicited by these treatments may be aid in identifying new targets in treating leukemia. Toxin £^ inducing cell death is found to evoke p38 MAPK-mediated Bcl-2 down-regulation, which facilitates mitochondria dysfunction, ROS generation and cytiochrome c release. Finally, activation of caspases leads to apoptotic death of toxin £^-treated cells. Piceatannol elicits Ca2+/p38£\ MAPK- mediated c-Jun and ATF-2 phosphorylation, leading to up-regulation of Fas/FasL protein expression and autocrine Fas-mediated death pathway activation. Caffeine treatment down-regulates MMP-2/-9 down-regulation via Ca2+/ROS-mediated inactivation of ERK/c-Fos and activation of p38 MAPK/c-Jun pathway. Consequently, caffeine treatment suppresses invasion of leukemia cells. PILP-1-induced ADAM17 down-regulation suppresses Lyn-mediated Akt phosphorylation, resulting in death of PILP-1-treated leukemia cells. Taken together, the results of the present study elucidate the signaling pathways responsible for apoptosis and invasion of leukemia cells. Moreover, these findings might suggest new targets in developing therapeutic strategy in treating leukemia.