Abstract: The relationship between enhanced anoxic tolerance induced by hypoxic preconditioning and mitochondrial membrane potential (MMP) was studied in cultured hypothalamic cells. Dynamic changes in MMP were monitored by confocal laser scanning microscopy and expression of B-cell lymphoma/leukemia-2 (bcl-2) was examined by flowcytometry. Hypoxic preconditioning increased the cell survival rate and decreased the lactate dehydrogenase leakage under acute anoxia, in addition to maintaining MMP at a relatively higher level and inducing bcl-2 overexpression during anoxia. The results suggest that hypoxic preconditioning can enhance the tolerance of hypothalamic cells to anoxia, and the underlying mechanism may be related to increased stability of MMP. Overexpression of bcl-2 induced by hypoxic preconditioning may play a role in sustaining the stability of MMP.