The present invention provides a plant protection agent and a method for improving plant salinity tolerance. In which, the plant protection agent contains an effective amount of a cyclic peptide: Cyclo(L-Ala-Gly). By administering the plant protection agent to a plant, the present invention may protect the roots and leaves of the plant from being influenced by a high salinity environment to continue to grow.本發明係提供一種植物保護劑及提高植物鹽度耐受性之方法，其中，該植物保護劑係包含一有效量之環肽：Cyclo(L-Ala-Gly)，而藉由投予該植物保護劑至一植物時，能夠保護該植物之根、葉等部位免於受到高鹽度環境之影響，而能持續生長。
