This review describes the evaluation of molecular state of medicines by using differential scanning calorimetry (DSC). Thermal behavior of amorphous clarithromycin obtained by grinding and spray drying were evaluated. In DSC curves, both broad and sharp peaks for crystallization were observed in 30 min ground sample, whereas spray-dried sample showed one broad peak for crystallization. In order to study the physicochemical stability of amorphous cefditoren pivoxil, glass transition accompanying enthalpy relaxation was evaluated for the ground and spray-dried samples by means of modulated-temperature DSC. Glass transition temperature (T_g) and relaxation enthalpy of the ground sample of cefditoren pivoxil were changed by storage for definite intervals at a temperature below T_g, while those of the spray-dried sample indicated an almost constant value by storage. These results suggest that the ground sample was less stable than the spray dried sample. The ground sample might be stabilized by storage below T_g. Thermal behavior of salicylamide in the mixtures with Folded Sheets Mesoporous Materials (FSM)-16 was investigated by DSC. Three kinds of molecular states of salicylamide, i.e., crystalline state, disordered crystalline state for which a broad endothermic peak was observed at a lower temperature, and amorphous state for which no peak on the DSC curves could be observed.