Diamonds can be used as dosimeters due to their high sensitivity to the ionizing radiation, radiation hardness as well as mechanical and chemical resistance. Moreover diamond, as the allotropic form of carbon, is tissue-equivalent what is an important property in regard to its potential future application in medical physics. Diamond films deposited on Si substrates by chemical vapor deposition (CVD) method using SEKI plasma reactor at the Institute of Nuclear Physics in Krakow were investigated to the aspect of their thermoluminescent (TL) properties. The deposition was performed at different oxygen concentration and the thermoluminescence of diamond films was studied. All grown diamond films were characterized in terms of surface morphology (scanning electron microscopy), chemical (Raman spectroscopy) and structural properties (X-ray diffraction). The influence of three types of radiation: α (241Am, 5.49 MeV), β (90Sr/90Y, 2.27 MeV), γ (60Co, 1250 keV) on the shape of the TL curves was also examined.