Microwave-assisted extraction(MAE) of polysaccharides from watermelon seeds and its monosaccharide composition by GC-MS was studied.The four parameters,extraction time,microwave power,extraction temperature and the ratio of solid to water were optimized using the Box-Behnken design(BBD) and the quadratic regression model was built by response surface methodology(RSM).The optimal extraction conditions for were as follows: extraction time19.5 min,extraction temperature 62℃,ratio of raw material to liquid 1∶ 0.9,microwave power 302W.Under the above conditions,the highest yield was 4.58%.The polysaccharides were characterized by FT-IR.The peaks appeared at 3 408 cm-1,2 928 cm-1,1 645 cm-1,1 408 cm-1,1 074 cm-1.The result of GC-MS showed that polysaccharides was mainly composed of six monosacharides: rhamnose,arabinose,xylose,mannose,glucose,and galactose and the molar ratio was 4.48∶ 13.14∶ 4.16∶ 7.82∶ 10.1∶ 60.3 respectively.