The most appropriate method to preserve Bufferin 81-mg tablets dispensed for unit-dose packaging in the hospital pharmacy was examined. The surface color change of the tablets was investigated over time by spectrophotometry, and the decomposition rate of aspirin was measured by high-performance liquid chromatography (HPLC). To overcome these, it was found that we can effectively prevent color changes and preserve the quality by maintaining the humidity as 55% or less, storage with drying agent in a plastic or aluminum pack. It was revealed that the color changes became greater and the decomposition rate became higher as time passed. Color changes markedly affect the patients' compliance, and are found to be a very important factor. It was considered that the clarity of the correlation between the color change and decomposition rate may contribute to a decrease in the number of tablets discarded before the expiration date.