In order to identify the morphological changes of tissues in mouse after irradiation. We have observed the redistribution of LDH isozymes and the morphological changes of skeletal muscle, heart, kidney, liver and testis in mouse according to variation amount with the time after the 1 Gray and 3 Gray irradiation each. As a result of H-E (hematoxylin-eosin) stain, the apoptotic bodies were more easily observed in the liver than the other tissues and the quantity of the apoptotic bodies was proportionated to radiation amount. The number of apoptotic bodies was shown the highest at 1 day in most tissues and at 7 day in testis after irradiation. TUNEL (terminal deoxyribonucleodtidyl transferase-mediated dUTP-digoxigenin nick end labeling) staining was shown the same results as H-E staining. After the irradiation, the protein content was reduced in tissues except kidney. And protein content was reduced in all tissues at the initial period of 2 hours after 3 Gy irradiation. But it increased at 7 days after irradiation. LDH (EC 1.1.1.27, lactate dehydrogenase) activity was increased mostly in tissues at the early stage after 1 Gy irradiation. The maximum activity was detected earlier stage after 1 Gy irradiation than 3 Gy irradiation. The activity of LDH $A_4$ isozyme was decreased in the skeletal muscle, heart, kidney, and testis. The activity of $B_4$ and $A_2$$B_2$ sozyme was increased in the skeletal muscle and heart, and the activity of heterotetramer isozyme was increased in kidney The activity of $A_4$ isozyme in liver was detected high level and the activity of isozyme including subunit C elevated in testis. Therefore, LDH isozyme seems to play a role of lactate oxidase in most tissues except liver after irradiation. These data support that LDH isozyme is predomintly involved in the aerobic metabolism.