In this study, purification, preliminary characterization, immunostimulatory and hepatoprotective activities of polysaccharides from Glossaulax didyma (GDPS) were investigated. Firstly, crude GDPS was purified by chromatography of DEAE-52 and Sephadex G-100, resulting in three purified fractions of GDPS-1, GDPS-2 and GDPS-3. The three fractions were mainly composed of glucose with the average molecular weight of 161, 197 and 204 kDa, respectively. GDPS-2 was quite different from GDPS-1 or GDPS-3. It had much higher contents of protein and sulfuric radical. For immunostimulatory activities in vitro, the three fractions could significantly stimulate the proliferation of splenocytes and enhance phagocytic activity of peritoneal macrophages. For hepatoprotective activity in vivo, the administration of GDPS significantly decreased the serum levels of alanine aminotransferase, aspartate aminotransferase and tumor necrosis factor-alpha, inhibited the formation of malondialdehyde and restored the liver activities of superoxide dismutase and glutathione peroxidase in Bacillus Calmette-Guerin/lipopolysaccharide-induced liver injury mice. The results suggested GDPS should be a potent natural polymer with immunostimulatory and hepatoprotective activities. Copyright © 2013 Elsevier Ltd. All rights reserved.