There is no account that directly describes the natural disaster in Balhae. But several incidents in which the Balhae's diplomatic missions to Japan were shipwrecked have been conveyed in the Japanese historical accounts, and some of them seem to have been caused by natural disasters. In this paper, the author examines the cause of the shipwreck of the second mission led by SeoYodeok in order to make some remarks on the natural disaster in Balhae. 　SeoYodeok who accompanied Heguri no Hironari(平群廣成) sailed for Japan between June and August in the eighth year of the Tempyo(天平) era. He encountered rough waves during the voyage, and his ship sank. This incident happened between July and September under the current Gregorian calendar, and when typhoons frequently pass near the Sea of Japan. Thus he was killed by a natural disaster, a typhoon.