The ultimate aim of developing a novel expandable gastroretentive drug delivery system was to synergy the swelling index of swellable polymers with combination of several swelling functionalities in the unit.In this study, the investigation of different type of swellable polymers and addition of ionic complex of polyelectrolytes on the swelling behavior was conducted.Physical characterizations of the tablets including swelling index based on weight variation and visual swelling observations were carried out.Among four different grades of HEC 250 (H, HX, HHX, and M),HEC 250HHX exhibited the greatest swelling index.Lower molecular weights PEO, varying from MW 100K to MW 900K, exhibited low swelling index and nearly dissolved after 2 to 4 h immersed in the medium.However, the swelling ability of PEO (MW 8000K) was found to be sustainable to an extent greater than that for HEC 250HHX.Combination of lower molecular weight PEO (MW 900K) with HEC 250HHX showed lower swelling index than that for HEC 250HHX alone,whereas when higher molecular weight PEO (MW 8000K) incorporated with HEC 250HHX resulted in higher swelling rate.On the other hand, the addition of ionic complex of polyelectrolytes showed only slightly improvement in swelling index.