Monosodium glutamate (MSG) is a sodium salt of glutamic acid, a naturally occurring non-essential amino acid. It is used as a food additive. It has the E number E621. The metabolic abnormalities and oxidative damage induced many diseases under the effect of monosodium glutamate (MSG) hazard, which is flavor enhancers used as an ingredient in various food products. The aim of this study is an assessment hazard of MSG by some biochemical and statistical analysis on serum rats. The rats were divided into 2 groups, each group contained 20 rats. The period of this study is four weeks. The first group is (control group) drinking water. The second group is (treated group) injected (4mg/kg B.W.) intraperitoneal (I.P.) of pure MSG from first week to third week and withdrawal in fourth week. After each week were anesthetized the rats with ether and blood was collected from the eye, for some biochemical analysis in heart, liver and kidney function tests. The present results revealed that chronic administration of MSG caused metabolic dysfunction characterized by the oxidative tissue damage by change in serum activities of aspartate aminotransferase, alanine aminotransferase, g-glutamyl transferase (GGT), alkaline phosphatase and creatine phosphokinase. The results also showed change in serum levels of Total bilirubin, creatinine, blood urea nitrogen, uric acid, glucose, cholesterol, triglycerides and low density lipoprotein with concomitant decrease in the high density lipoprotein compared with control group from first to third week, but after withdrawal of MSG, most of these tests have improvement results. Finally, MSG may cause an adverse effect on the liver and kidney and heart function tests which might be due to oxidative stress. We recommended decrease or prevention added of MSG as a flavor on food to become better hazard effect.