An efficient microwave-assisted extraction (MAE) technique was developed to extract polysaccharides from Enteromorpha prolifera (PEP). The operating parameters, such as microwave power, liquid/material ratio, temperature and extraction time, were optimized using orthogonal array design coupled with single factor method. PEP yield was determined by the phenol-sulfuric acid method. The optimum extraction conditions were determined as follows: microwave power, 700 W; liquid/material ratio, 40:1 (mL/g); temperature, 70 °C; and extraction time, 25 min. Under such conditions, PEP yield reached to 10.79 %. In comparison with conventional hot water extraction and ultrasonic-assisted extraction, MAE showed obvious advantages in terms of high extraction efficiency, saving energy, rapidity, solvent consumption, and so on. The data demonstrated that MAE could be a fast and reliable method for quantitative analysis of PEP. The scavenging capability of PEP to DPPH/hydroxyl radical reached to 65.2 % and 41.2 % at the concentration of 0.5 mg/mL. The reducing power of PEP was 0.354. Compared with butylated hydroxytoluene (BHT) and gallic acid (GA), the experimental results showed that DPPH radical scavenging activity of PEP was higher than that of BHT. Thus, PEP had good potential as a natural antioxidant used in functional food or medicine industries.