A study was made on preparation of cation-exchange membranes including sulfonate and carboxylic acid groups by pre-irradiation grafting of acrylic acid (AA) and sodium styrene sulfonate (SSS) onto high-density polyethylene (HDPE). The grafting yield was strongly dependent on the synthesis conditions such as concentration and pH of the monomer solution, grafting temperature and type of solvent. An easy control over the grafting yield could be achieved by proper selection of reaction conditions. Water absorbance of grafted membranes increases with increasing grafting yield.