Abstract: The experiment was conducted to investigate the effects of dietary magnesium asparatate (MgAsp) supplementation on lipid peroxidation status in the liver and the thigh muscles of broiler chickens and its possible mechanisms. One hundred and twenty eight 22-day-old male AA broiler chickens were allocated into two treatments, each treatment with eight replicates of 8 chickens. The maize and soyabean meal are the main ingredients of diet in control group, and the diet supplemented with 1% MgAsp served as the diet of experimental group. At 42 days old, one of each replicate was slaughtered. Serum, thigh muscle and liver were collected. Results showed that, compared with the control group, the Mg concentration of serum, thigh muscle and liver in broilers fed with Mg supplementation diet increased by 22%, 21% and 29% (P<0.01), respectively; Malondialdehyde (MDA) contents of liver and the thigh muscle decreased by 24％(P<0.01) and 29％(P<0.01), respectively; Hepatic catalase (CAT) and total superoxide dismutase (SOD) activities increased by 25％(P<0.01) and 14％(P<0.05), respectively; The thigh muscle CAT activity increased by 37％(P<0.01); Dietary Mg supplementation significantly decreased reactive oxygen species (ROS) production in the thigh muscles(P<0.01); There was no difference in the total content of unsaturated fat acids between two groups (P>0.05). These results suggested that MgAsp supplementation in the diets based on maizesoyabean could decrease lipid peroxidation level in the liver and the thigh muscles of broiler chickens; Enhanced CAT activity and decreased ROS production in the thigh muscle lead to the decrease of lipid peroxidation level, however it is the enhanced hepatic CAT and SOD activities not ROS production that decreased lipid peroxidation level in the liver of broiler chickens.