Abstract: The respiratory metabolic changes in mung bean seedling cotyledons during senescence were as follows. (1) The respiratory rate of cotyledons of mung bean seedlings decreased rapidly during senescence in cotyledons because of a depletion of respiratory substrates in the cotyledons. (2) With the changes in mitochondrial structure of senescent cotyledons, the ADP/O and RC decreased. However, the oxidative activity of isolated mitochondria by adding L-malate, a-ketoglutarate, succinate and NADH and the cyanide-resistant respiration increased. (3) The catalitic activity of mitochondrial ATPase was transformed from synthesizing ATP into hydrolyzing ATP. The decay in oxidative phosphorylation and the transformation of ATPase were related with the changes of mitochondrial structure and resulted in the energy deficiency of the cotyledon cells and therefore accelerated the deteriorative processes of the cotyledon senescence.