The state of the mitochondrial megapore (mitochondrial permeability transition pore-mPTP), respiration and oxidative phosphorylation of rat liver and pancreas mitochondria in streptozotocin (STZ) -induced diabetes were studied, considered the ways of correction of the detected membrane damage with the flavone luteolin isolated from the plant Inula caspica. It was shown that, under conditions of experimental diabetes mellitus, the rate of swelling of rat liver and pancreas mitochondria is higher than of the healthy ones; this means that mPTP of rat liver and pancreas mitochondria is in the open state in pathology. Luteolin recovers mPTP to the normal condition, thus removing the effect of STZ on mitochondria. It was also shown that, the respiration rate of liver and pancreatic mitochondria in the state 3 and state 4 states increases in STZinduced diabetes, which significantly reduces the respiratory control (RC) and ADP/O coefficients in comparison with the control. The data obtained indicate the disconnection of respiration and oxidative phosphorylation in STZ -induced diabetes. Luteolin (oral dose is 50 mg/kg of body weight, during 8 days) eliminates the detected functional disorders of rat liver and pancreas mitochondria, probably due to its antioxidant properties.