The origin of charge carrier traps in ZrO2 films was studied using charge transport measurements, EPR spectroscopy and quantum-chemical calculations. After the X-ray irradiation of the ZrO2 films, the EPR spectra from an interstitial oxygen and a negatively charged oxygen vacancy are observed. The trap thermal and optical activation energies 1.25 eV and 2.5 eV are estimated from the charge transport measurements. Within experiments on the extraction of minority carriers from silicon substrates, it was demonstrated that both electrons and holes can be trapped on oxygen vacancies in ZrO2. Hence, oxygen vacancies are supposed to operate as traps responsible for the charge transport in ZrO2 films.