Ultrasound-assisted extraction was employed to extract polysaccharides from lotus (Nelumbo nucifera Gaertn.) seeds. Response Surface Methodology was used to determine the optimal extraction conditions of ultrasound power, extraction time, and extraction temperature at 406 W, 7.7 min, and 94 degrees C, respectively. The crude extract was successively purified by chromatography, yielding a major polysaccharide fraction termed LSPS-1. It is a heteropolysaccharide, containing rhamnose, arabinose, glucose, and galactose with a molecular weight of 4484 Da and an alpha-dominating configuration in pyranose form sugar. Preliminary antioxidant activity test in vitro showed LSPS-1 could potentialize the scavenging effect on hydroxyl radicals in a dose dependent manner.