The characters '長屋親王宮鮑大贄十編' (Ten abalone were contributed to the Imperial Prince Nagaya) were printed on a mokkan excavated from the site of the residence of Prince Nagaya and he was called 'Imperial Prince Nagaya' in an episode regarding Nagayao no Hen in "Nihon Genho Zen-aku Ryoiki" (set of three books of Buddhist stories, written in the late 8th and early 9th century, usually referred to as the Nihon Ryouiki), so there is a theory which states that he was called Imperial Prince Nagaya when he was alive.
長屋王の邸宅跡から発掘された木簡に「長屋親王宮鮑大贄十編」の文字があったこと、『日本現報善悪霊異記』の長屋王の変に関する説話では「長屋親王」と称されていることなどから、在世時には長屋親王と称されていたとする学説もある。