The effect of quercetin (QRT) in preventing or reducing the diclofenac sodium-induced gastric ulcers was evaluated in rats following over night fasting by using a scanning electron microscopy. The scanning micrographs of stomach specimens showed a marked reduction in the gastric ulceration only when the quercetin is given before the administration of diclofenac sodium. The physicochemical characteristics of diclofenac sodium and quercetin combination were studied using differential scanning calorimetry, IR spectroscopy and X-ray diffractometery. The results revealed that a chemical incompatibility of diclofenac sodium and quercetin undoubtedly has been occurred when they were mixed in one combination. According to aforementioned results, we advise orally taking quercetin only before administration of diclofenac sodium as a prophylactic treatment to protect against its expected gastric disturbances.