Recently, rapid and effective extraction and purification methods have attracted considerable interest as alternative approaches to conventional methods. In this study, ultrasonic-microwave-assisted extraction (UMAE) was used to extract GraciIaria lemaneiformis polysaccharides, and the response surface methodology was used to determine the optimum extraction conditions. Subsequently, an aqueous two-phase system (ATPS) was applied to the purification of crude polysaccharides. The chemical structure and anti-tumor activities of three fractions of purified G. lemaneiformis polysaccharides were also investigated. We found that the optimal condition for UMAE was 50 W of ultrasonic power, 31.7 min, 87 degrees C and at a solid-to-water ratio of 1.0:60.7 of extraction temperature. The extraction yield of polysaccharides reached 34.8% under optimum UMAE conditions. The crude polysaccharides were successfully partitioned in the intermediate phase with a recovery rate of 81.1% in an ethanol/ammonium sulfate system. After being fractionated by a DEAE Sephadex A-50 column, three polysaccharide fractions (GLP1, GLP2, and GLP3) were obtained, accounting for 14.3%, 65.2% and 20.6%, respectively. GLP1, GLP2 and GLP3 were mainly composed of galactose with molecular weights of 5.5 kDa, 85 kDa and 82 kDa, respectively. Those polysaccharides exhibited inhibition activity on MCF-7, HepG-2, and Hela cell proliferation in vitro, and GLP-3 exhibited the highest anti -tumor activities. These results indicated that UMAE and ATPS are rapid, efficient, and environmentally-friendly extraction and purification methods for marine algal polysaccharides. These G. lemaneiformis polysaccharides could potentially be used as anti-cancer adjuvants in conjunction with pharmaceutical therapies.