Background: Oxidative stress is defined as condition when  reactive oxidative species generation  exceed  the physiological  level,  and overcome  the antioxidant  capacity  which  lead to  biomolecules damage,  excessive  peroxidation of lipid, damage of DNA strands  ,impairs gene expression,  mitochondrial dysfunction and  play a  main role in the pathophysiology of  many diseases. Aim of the study: This study was aimed to investigate protective role of N-acetyl cysteine (NAC) as antioxidant on mitochondrial gene expression and copy number against oxidative stress damage in salivary glands Material and Methods: Forty adult male albino rats were used in this study.  Animals were divided into 4 groups: Group1 (Control negative, n=10): Normal diet and tap water for drinking intraperitoneally for 4weeks. Group2: (Control positive, H2O2) (n=10) normal diet and drinking water contain 0.5% H2O2 daily to induce oxidative stress for 4weeks. Group3: N-acetyl cysteine (NAC, n=10) normal diet and tap water for drinking injected daily with  NAC 150 mg /kg (i.p.) For 4weeks. Group4: (Protected  group) (NAC+H2O2) (n=10)  normal diet and  drinking water contain 0.5%  H2O2 daily to induce oxidative stress, injected daily with NAC 150 mg. /kg ( i.p.) for 4weeks. Tissues were collected after 4 weeks of experiment, all animal groups were euthanized and salivary glands were removed for genomic and histopathologic study. Result: The results showed that oxidative stress induced by H2O2 cause significant reduction in the mitochondrial copy number in salivary gland tissue and induce severe necrosis and degeneration in control positive group while protected group with NAC showed no significant changes in mitochondrial copy number and no necrosis or degeneration in salivary gland tissue Conclusion: N-acetyl cysteine protects the mitochondrial copy number of salivary glands from  reduction by oxidative stress and  prevents histopathological changes.