Intrinsic ability to memorize heat stress is crucial for plant survival under extremely high temperatures. Among sessile aquatic seaweeds, establishment of heat-stress memory has been confirmed only in the filamentous red alga ‘Bangia’ sp. ESS1. By memorizing exposure to nonlethal high temperatures, this alga can survive under temperatures that would be lethal in its native environment, even after a period of recovery under normal growth conditions before exposure to lethal temperature. This finding indicates the presence of memorization ability in ‘Bangia’ sp. ESS1. Herein, we describe our methods for confirming the intrinsic ability of Bangiales species to acquire heat-stress tolerance and establish heat-stress memory by presenting our novel findings of the ability to memorize heat stress by the foliose red alga Pyropia yezoensis.