Ultraviolet (UV) radiation is able to cause biological changes at the cellular and molecular level. These biological structures are nano- and micro-sized, so to study the effect of UV radiation, detector is required, commensurate with their size. Ferroelectric P(VDF-TrFE 70:30) films deposited on a glass substrate were examined as a possible sensor of UV radiation. Changes in surface electric potential of the P(VDF-TrFE 70:30) films under UV radiation were investigated by Kelvin force microscopy. The hypothesis was proposed that UV radiation was well absorbed by the glass substrate changing its surface charge. This charge changed polarization of the films leading to changes in their surface electric potential. It was found that after 6 minutes of UV irradiation surface electric potential of the P(VDF-TrFE 70:30) films decreased and no changes were observed further increasing irradiation time. However, surface electric potential of the bare glass substrate continued to decrease increasing irradiation time. It was also found that surface electric potential of the P(VDF-TrFE 70:30) films relaxed to its initial value within half an hour after the irradiation was stopped. The relaxation obeyed exponential law. Ability of the examined P(VDF-TrFE 70:30) films deposited on the glass substrate to change their polarization upon application of external DC bias voltage was also checked by Piezoresponse force microscopy. The DC bias was used as a model for electric charge induced on the surface of glass substrate during UV irradiation.