Abstract: The epidemiologic studies indicated that there was an inverse association between blood seleniun level and the morbidity and mortality of many types of cancer,Animal experiments also showed that selenium supplement may inhibit oral cancer.In this study fifty-four patients with oral cancer confirmed by pathologic examinations were supplemented with 900μg of selenium daily,for ten days in the pre-operative period.We found plasma selenium （Se）and the activity of plasma glutathione peroxidase（GSH-Px）increased significantly and the concertrations of lipid peroxides（MDA）decreased after treatment.With the paired comparision,a statistically signifcant difference（^P＜0.01）was found.The tumor mass decreased in some degree in some patients.