Thermal analysis is commonly used in the pharmaceutical field because it is an important tool in the solution of problems involving development, production and quality control of medicines. This paper presents the thermal behaviour of six anticancer active derivatives of 3-(2-furanyl)-8-aryl-7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-one. The samples were characterized by the TG–DSC and TG–FTIR analyses. The studied compounds are stable at room temperature which is important for medical application. The TG analysis under dynamic air atmosphere revealed that thermal degradation of the compounds starts above 300 °C and proceeds in two steps. The melting processes of compounds are observed before starting their decomposition or at the beginning of their combustion. Pyrolysis processes under nitrogen atmosphere take place in single or two steps. The major pyrolysis gaseous products identified are ammonia, carbon dioxide, isocyanic acid and its derivatives, hydrogen cyanide, aniline or its derivatives and carbon monoxide.