The present invention provides eluent for ion-exchange chromatography, wherein the eluent allows separation and detection of a target nucleic acid such as a PCR-amplified product, a restriction enzyme fragment of the PCR-amplified product, or a restriction enzyme fragment of a nucleic acid in a short time with high separation performance. The present invention also provides a method of analyzing nucleic acid chains by ion-exchange chromatography using the eluent. The present invention provides an eluent for ion-exchange chromatography comprising a guanidine salt derived from guanidine represented by the following formula (1):;
