Background: Diazinon is one of the most toxic organophosphrous pesticides. It is used widely in agriculture and affects the general health and the economy of the human. Toxic effect of Diazinon is due to inhibition of acetylcholine esterase, an enzyme needed for proper nervous system function. This study was designed to investigate the effects of Diazinon on the liver tissue and the expected protective role of vitamin C. Aim of this study: is to evaluate effect of Diazinon and vitamin C on liver of albino rats. Results: data showed a significant increase in liver enzymes AST, ALT in addition to GGT and decreased total proteins and albumin as well as different histological changes caused by the pesticide Diazinon. Using vitamin C caused amelioration in liver structure and function tests, although, all these tests did not return to the normal level. Conclusion: the present study proved that Diazinon has adverse effects on some biochemical parameters and liver functions leading to histological impairment and these effects increase with the increased time of exposure. Meanwhile, supplementation with vitamin C could ameliorate the adverse effects of Diazinon.