Abstract: The purpose of the present study was to examine the separate and the combined effects of lead and hyperoxia in adult rats, Ratus ratus on LDH. Thirty-two rats were assigned randomly to control (C) and three experimental groups: lead (BP), hyperoxia (HP) and Hypaeroxia-Lead (HPBP). The mean (±SEM) activity of LDH rose significantly (p<0.05) from 216.41±12.39 U L-1 in control group to 539.28±28, 512.78±16.09 and 465.94±55.88 in BP, HP and HPBP groups, respectively. Therefore, both the separate and the combined effects of heavy metal lead and hyperoxai involve activation of LDH to compensate for cellular changes in the cytoplasm. Based on the results of the present study, it can be concluded that lead induces similar effects to hyperoxia exposure that causes the formation of Reactive Oxygen Species (ROS) which mediate changes in the cytoplasm enzymes such as LDH in rats.