Abstract: Microwave-assisted extraction(MAE) technique and free radical scavenging activity of β-carotene of Dunaliella salina were investigated. Acetone was used as extraction solvent,the optimum conditions were as follows:microwave power 500 W,ratio of liquid to solid 250 m L/g,extraction temperature 40 ℃,extraction time8 min,and stirring time 180 r/min,under the optimal conditions,β-carotene yield of Dunaliella salina was 1.13%which was higher than that of conventional maceration solvent extraction(MSE). Three kinds of in vitro antioxidant system(reducing power,hydroxyl radical scavenging,and anti-lipid peroxidation activity) results showed that there was no significant difference(p>0.05) between β-carotene extracts of MAE method and conventional maceration solvent extraction method for free radical scavenging capacities( such as the reducing power,hydroxyl radical scavenging,and anti-lipid peroxidation activity). But the free radical scavenging capacities of two extraction methods were all higher than that of β-carotene standard solutions. It was indicated that there were other substances with good antioxidant activity in Dunaliella salina extracts,but the antioxidant effects of Dunaliella salina extracts were all lower than those of ascorbic acid or BHT.