The aim of the research is to design a dosimeter that provides measurements of doses of ionizing radiation absorbed in nano-sized objects. Such dosimeters can be useful for radiobiology in order to study effects of radiation on nanosized biological structures such as DNA molecule. We offer to use radiation-sensitive semiconductor nanoparticles as nanosized active elements of the dosimeter. Nanoparticles have to be embedded into a dielectric matrix that provides physical and chemical stability of the nanoparticles. Ionizing radiation can change concentration of electrons on localized levels of dosimeter material. Therefore, readout of the absorbed dose can be provided by measurements of photoelectron emission (PE) from the dosimeter. Lead sulphide (PbS) nanoparticles having diameters of 2.5–4.5 nm embedded in a matrix of zirconium oxide (ZrO2) by sol-gel technology [1] were studied (ZrO2:PbS films). The films were irradiated with 0–10 Gy of 9 MeV electron radiation generated by a medical linear accelerator. It was found that PbS nanoparticles create active PE centres in ZrO2:PbS film. Concentration of the active PE centres decreases under influence of ionizing radiation.