This study demonstrated that stability and excipient compatibility of solid dosage form could be estimated by the isothermal microcalorimetric method. Flavoxate Hydrochloride and Oxbutynin Hydrochloride were used as a model drug of stability and excipient compatibility, respectively. Evaluation of stability and excipient compatibility of solid dosage form by the acceleration test may be possible to use the new method by the isothermal microcalorimetry instead of that done at present. By using these methods, the stability prediction of drug and evaluation of the compatibility between drug and excipient can be measured by a simple operation in a short time. Application of the isothermal microcalorimetry would be useful for the screening test for the drug stability.