In an electrolyte of a non-aqueous electrolyte secondary battery using a cyclic carboxylic-acid ester exerting high conductivity under a low temperature condition, for suppressing reductive decomposition of the cyclic carboxylic acid ester, a cyclic carbonic acid ester having at least one carbon-carbon unsaturated bond is contained, and for suppressing excessive polymerization reaction of the cyclic carbonic acid ester having at least one carbon-carbon unsaturated bond, a cyclic carbonic acid ester having no carbon-carbon unsaturated bond is further contained.