The applicability of chitin and chitosan for prolonged-release preparations of a water soluble drug was examined. In this study, the dissolution behavior of physical and ground mixtures of p-aminosalicylic acid(PAS), a water soluble drug, with chitin and chitosan was investigated. The intensity of powder X-ray diffraction pattern in a ground mixture (GM) was smaller than that of a physical mixture (PM), suggesting a relative decrease in the size of the crystals of PAS in the ground mixture. The dissolution rate of PAS from the ground mixtures was significantly slower than that from the physical mixtures or from pure PAS powder. Particularly, the ground mixture with chitosan showed the slowest dissolution. These results indicated that the 1:2 ground mixing ratio of PAS-chitosan mixture might be suitable and the results obtained at this ratio could be practically useful, because of the amount of excipient should be small for formulation.