Aloin is a physiologically active anthraquinone present in aloe. There are two isomers of aloin, aloin A and aloin B, occurring as a mixture of diastereomers. The objective of this study was to determine the bioavailability and tissue distribution of aloin. Rats were gavaged with 11.8g/kg aloin, and the levels of aloin and its conjugates were measured in plasma, tissues, and urine. Plasma aloin level showed a peak at 1hr after the administration and the concentration was $59.07{pm}10.5;ng/ml$. The 24 h cumulated urinary aloin was 0.03% of the initial dose. These results suggest that aloin is absorbed and reaches a peak plasma level within 1-1.5 h after the administration and a significant portion is possibly metabolized or is excreted in feces. These results can apply to the determination of the adequate intake level of aloe and aloe products to achieve the desired biological effect, and to interprete in vitro study results.