Response surface methodology( RSM) was used to optimize the extraction condition of crude polysaccharides( WJc) from Brassica rapa L.. Three independent variables of extraction temperature( ℃),extraction time( h),and ratio of water to raw material( mL/g) were investigated. The experimental levels were determined by singlefactor tests. The optimum conditions were as follows: extraction temperature 80℃,extraction time 2. 5 h,liquid /solid ratio 30 mL /g. Under these conditions,the experimental value was 8. 858%,which was very closed with the predicted valuel. In vitro,free radical scavenging activities results indicated that WJc were found to be effective in scavenging hydroxyl radicals. Overall,WJc may have potential applications in the medical and health food.