Disclosed is a non-aqueous electrolyte comprising: a non-aqueous cyclic solvent; a catalyst for polymerization, which is activated depending on temperature or voltage to induce the polymerization of the non-aqueous cyclic solvent; and an electrolyte salt. Also, a secondary battery comprising the non-aqueous electrolyte is disclosed. The non-aqueous electrolyte does not influence the performance of the battery at the normal operating temperature and voltage of the secondary battery. However, when the battery misoperates due to high temperature or overcharge, the polymerization of the non-aqueous cyclic solvent can occur due to the catalyst for polymerization contained in the non-aqueous electrolyte, at a specific temperature or voltage, to increase the resistance of the electrolyte and reduce the ion conductivity of the electrolyte, thus increasing the safety of the battery.