Introduction:  Nanoparticles have different effects on humans as  they have  specialized characteristics from the bulk materials.  Zinc oxide nanoparticles are most commonly utilized nowadays due to their unique characteristics. On the other hand Zinc oxide nanoparticles have been found  to have adverse effects on humans as cytotoxicity so it is a double-edged sword. Quercetin is a flavonol with beneficial anti-oxidant and antiinflammatory effect. Aim :The present work aimed to investigate the effects of Zinc oxide nanoparticles on rat submandibular glands and to evaluate the prophylactic effect of Quercetin . Materials and Methods: Twenty four male rats were equally divided into three groups: group A control, group B treated with Zinc oxide nanoparticles and group C treated with   Zinc oxide nanoparticles and Quercetin for twenty eight  days. Results: At the end of the study, rats were sacrificed and the effects of Zinc oxide nanoparticles as well as the prophylactic role of Quercetin on the submandibular glands were evaluated by light microscopy. The cells of the acini  in group B revealed signs of cytotoxicity as loss of the acinar architecture, apoptotic nuclei, and cytoplasmic vacuolation while, in group C submandibular glands showed accentuated preservation in the cells of the acini and ducts that was comparable to that of the controls. 
Conclusion: This experiment clarified that Zinc oxide nanoparticles has a cytotoxic effect and illustrated that prophylactic administration of Quercetin efficiently counteracted the toxic effect of Zinc oxide nanoparticles administration in rat models. Therefore, Quercetin can be prophylactically used to prevent Zinc oxide nanoparticles cytotoxicity.