The main purpose of our study was to produce microspheres containing diltiazem hydrochloride and to perform the thermoanalytical examination of the components and microspheres. Thermal analysis is a very frequently used method in the preformulation tests of solid dosage forms. Diltiazem hydrochloride is a calcium-channel blocker with short biological half life, so it is a potential candidate for sustained or controlled release dosage forms. Various techniques are available for the microencapsulation of drugs. The technique of spray-drying was used during our investigations. It was found that the crystalline form of the active agents could not be observed in the drug-loaded chitosan microspheres, which indicates the molecular dispersion of the drug in the matrix. It was established that the preparation conditions influenced the morphology and size of the particles. Moreover, the sphericity of the microspheres was good. On the basis of our investigations, the 1:1 diltiazem hydrochloride–chitosan ratio is suggested as the best ratio.