Ryōsan 良算 (b. 1202, date of death not securely established) was a mid-Kamakura-period Japanese Hossō 法相 scholar-monk affiliated with Kōfuku-ji 興福寺, working in the doctrinal lineage continuing Jōkei 貞慶 (1155–1213). His principal surviving work is the monumental KR6n0018 Yuishikiron dōgakushō 唯識論同學鈔 (T2263, 68 fasc.), a mondō-format Hossō study-record on the Chéng wéishí lùn that is the single longest Hossō text in the Taishō supplements.
Ryōsan stands within the Hokuji 北寺 (“Northern Temple”) faction of Kōfuku-ji Hossō — the Genbō / Chitsū / Dōshō lineage that had imported the Wŏnch’ŭk-line of Silla Yogācāra alongside the standard Kuījī-line Cí’ēn tradition. His Dōgakushō preserves over 230 citations of Wŏnch’ŭk 圓測 (613–696) plus extensive citations of Sinbang 神昉, Wŏnhyo 元曉 (617–686), and Kyŏnghŭng 憬興, making it the principal medieval-Japanese witness to the Silla Yogācāra reception.
DILA Buddhist Person Authority A000542. Principal scholarship: A. Charles Muller and Ronald S. Green, “Early Japanese Hossō in Relation to Silla Yogācāra” (various venues); Fukushi Jinin 福士慈稔 on Ryōsan’s Silla citations.