Phaya Leuthai, Lu Thai, Sri Suryavamsa Rama Mahadharmarajadhiraja, also known as Phra Maha Thammaracha II, is a king of the Sukhothai Kingdom, succeeding his father in 1347.

He had composed the Traibhumikatha, Traiphum Phra Ruang, in 1345, while the viceroy of Satchanalai.

He also reforms the calendar in use.

In 1349, the armies from Ayutthaya kingdom, under Ramathibodi I invade, gaining the submission of Sukhothai.

King Lu Thai turns to religion, building temples and monasteries, and enters the order of Buddhist monks in 1361.