Most medicines except biological preparations are stored at normal temperature(1 5∼25℃) and served to patients. The shelf life of each medicine indicated variously. In this study, vitamin C tablet, vitamin C powder and prednisolone tablet of drugs sold were chosen. For examination of its stability and fitness of drugs, half-life and time required for drug potency to fall to 80% were studied by accelerated stability analysis. Prednisolone tablets have 1.28 year of shelf life at 25℃ but the tablet and the powder of vitamin C have faster destruction. As a result, it is necessary to adjust the storage temperature and the shelf life of the drugs.