This paper reports the thermal stability and thermal degradation of six derivatives of indole by means of TG-DSC (in air) and TG-FTIR (in nitrogen) techniques. The compounds were also characterized by infrared spectroscopy. In addition, IR spectra were calculated and compared with the experimental data. In particular, the potential energy distribution analysis was performed to assign IR signals. The studied compounds are characterized by good thermal stability in oxidizing and inert atmospheres which is important for potential medical application. Thermogravimetric measurements in air atmosphere showed that the decomposition of compounds proceeds in two or three main stages. The thermal degradation of compounds is preceded by the melting process. The pyrolysis of samples is a one-step process. Together with the analyses performed in nitrogen, the FTIR spectra of the evolved gas phase products were recorded. On the FTIR spectra of gaseous products, only the bands of water, carbon dioxide and carbon oxide molecules are present. In the case of indole derivatives containing the p-chlorobenzyl substituent in position 1, the bands of anisole, p-chlorotoluene and chlorobenzene also appear.