A monolithic osmotic tablet system (MOTS) with two orifices in both side surfaces has been studied. Water-insoluble naproxen was selected as the model drug. Gum arabic was used as an osmotic, suspending and expanding agent, and cellulose acetate (CA) was used as semipermeable membrane. Polyethylene glycol 400 (PEG-400) was employed as plasticizer for controlling membrane porosity. The influences of gum arabic, PEG-400, membrane thickness and orifice size on the naproxen release profiles were investigated, and the optimal MOTS was evaluated in different environment media and stirring rates. The optimal MOTS was found to be able to deliver naproxen at a rate of approximately zero order up to 12 h in pH 6.8, cumulative release at 12 h is 81%, independent on environment media and stirring rate. Therefore, this MOTS can be used in oral drugcontrolled delivery field, especially for water-insoluble drug.