A stability test is one of the tests which are required the longest time in a development of a drug. For quick release of new drugs to the market, it is indispensable to estimate stability speedily from exact information in preliminary stability tests, and to minimize idle time at an early developmental stage. However, it is technically difficult to predict exactly in a short time before a stability test, what decomposition will occur. We developed a new stability prediction method using thermal analysis to solve the problem. This method is very speedy; it only takes two weeks to predict stability of a drug substance in detail. The operations are simple; mainly thermal analysis and liquid chromatography. The method is performed by minimum 1 mg per measurement. And total amount of sample being necessary to predict stability is approximately 20 mg. The sample quantity is so little that the method can be used even at an early developmental stage when production scale is small. Furthermore, the accuracy and the precision of prediction using the method are equivalent to or better than those of 6-month preliminary stability tests. This method is very widely applicable to chemical materials including pharmaceutical raw materials, pharmaceutical intermediates, agricultural chemicals, and pesticides.