An investigation was performed of the liver mitochondrial respiratory function in rats after 1, 3 and 6 weeks of biliary obstruction and the following results were obtained: 1) Various parameters of liver mitochondrial respiratory function, such as respiratory control ratio, ADP/O, O₂ consumption in state 3 respiration and adenosine triphosphate synthesis were found to decrease with prolongation of biliary obstruction. 2) The mitochondrial respiratory enzymes, cytochrome a (+a₃) and cytochrome c(+c₁) showed that both decreased in contents with prolongation of obstruction, particularly the latter. 3) The activation ratio of ATPase (latent ATPase/dinitrophenol stimulated ATPase) was increased after long term biliary obstruction, which was thought to indicate the severe damage of mitochondrial membrane. 4) Investigation of the respiratory function with the various respiratory substrates showed that the locations of mitochondrial respiratory inhibition in obstructive jaundice are at sites 1 and 2, which is the same as the situation seen in nonspecific damage of mitochondria. 5) There was a high degree of mitochondria) respiratory disturbance by bile acids, particularly CDCA, which is thought to be one of the causal factors of liver dysfunction in obstructive jaundice. 6) Mitochondria] respiratory function was markedly disturbed in hypotension, and the degree of which correlated with length of time of biliary obstruction.