The jigo 'Onjo' was named by the Emperor Tenmu who was deeply impressed by the aspiration of Otomo-no-Yota-no-Okimi to establish a temple at the cost of his 'Shoen-joyu' (a private estate and a castle).
「園城」という寺号は、大友与多王が自分の「荘園城邑」（「田畑屋敷」）を投げ打って一寺を建立しようとする志に感じて名付けたものという。