The present invention is to provide a crystal of (S,E)-2-(2,6-dichlorobenzamido)-5-[4-(methyl-pyrimidin-2-ylamino)phenyl]pent-4-enoic acid having excellent chemical and physical stability, and a medical use thereof. The present invention provides a crystal of (S,E)-2-(2,6-dichlorobenzamido)-5-[4-(methyl-pyrimidin-2-ylamino)phenyl]pent-4-enoic acid.