This paper was designed to investigate the influence of different suppository bases on both the rectal absorption and dissolution rate of lithium carbonate, and to compare bioavailability from rectal administration with that from oral administration. The dissolution rates were in such order as PEG 4000, surfactant A (Witepsol 15+sodium lauryl sulfate), surfactant B (Witepsol 15+ cholic acid), Witepsol 15 and cacao butter. Among various suppository bases, the blood level of lithium carbonate after rectal administration was increased in the following order: surfactant A > surfactant B > PEG 4000 > Witepsol 15 > cacao butter. When it comes to compare oral with rectal administration in AUC values, surfactants and PEG 4000 showed similar blood levels to oral administration, but lipophilic bases such as Witepsol 15 and cacao butter showed far lower blood level than oral administration. Peak time in oral administration was 2 hrs, but those in rectal administration using various suppository bases were 6∼8 hrs.