An“electron leak route” is suggested to be present in the respiratory chain in mitochondria. The route consists of electron leaks:the one on the substrate side produces O2·- and H2O2,while that from one on the substrate side actually reduces H2O2 to H2O。Therefore,the “electron leak route”is actually function as a way of oxygen radical metablism. The O2·--conumption by the“electron leak route”is insensitive to KCN,and therefore can be considered as a way of non-phosphorylative respiration of mitochondria.