The subject of the invention is a device and a method for monitoring the condition of metal-oxide surge arresters installed in electricity distribution networks. Condition of metal-oxide surge arresters is monitored by measuring the resistive component of the leakage current flowing through metal-oxide surge arrester. The subject of the invention solves technical problems: precise measurements of leakage resistive component, correct compensation of external factors, especially temperature differences, the possibility of performing measurements at the installation site of metal-oxide surge arresters without disassembly and remote reporting of metal-oxide surge arresters condition to authorized places. Device for monitoring the condition of metal oxide surge arresters gathers measured values of the leakage current and ambient data. After digitization of the entire leakage current, the resistive component of the leakage current is extracted, the phase shift between current and voltage is reconstructed. The maximum value of the resistive component is sought and a comparison with preset values is performed. If the measured value of the resistive component is not in the pre-set value margin, an alarm is sent.