Hypoxemia during hemodialysis(H.D) was reported 1st in 1974. Many studies have confirmed occurrence of hypoxemia during H.D. We experienced of hypoxemia during H.D in liver transplanted patient who were treating ventilatory care. 1st case, we experienced significant drop of arterial O2 tension and recovered to pre-H.D level after H.D . We prevented drop of arterial O2 tension during H.D by prior supplement of increased inspired O2 in 2nd case. To a group of liver transplanted patients especially having limited cardiac and pulmonary reserve , H.D may produce severe complications. We concluded that monitoring of oxygenation should be done and supplemental O2 should be given before starting H.D in critically illed patients.