Background: The production by plants of compounds useful as medicines or raw materials for the manufacture of medicines is influenced by ultraviolet radiation.  Ultraviolet is, UV, very important when used to improve medicine products in plants.   No available studies covered the effect of UVC for a long period of time and its high power on the chemical composition and antioxidants of medical plants.  For this reason, the aim of this research is to study the effect of UVC on internal structure, enzymatic and non-enzymatic antioxidants for yellow mustard.  Methods: The irradiated system consists of a fluorescent lamp is used.  Pure Yellow mustard seeds (Sinapis alba) are used as research samples, received from the Egyptian Ministry of Agriculture.  Total phenols were determined calorimetrically by the Folin-Ciocalteu reagent.  UV/Vis spectrophotometer, Jenway, England was used to determine GSH.  Results: The chemical composition of yellow mustard is highly affected after exposure to UVC.  Glutathione in yellow mustard varied after being exposed to UVC.    DPPH scavenging activity for yellow mustard decreased but total phenolic content increased after exposure to UVC.  The results from scanning electron microscope and IR spectrum analysis showed the internal structures such as molecule arrangement, orientation and size or molecular bonds (as strength and position) for yellow mustard changed after exposure to UVC.