Wat Phra Si Rattana Mahathat (Thai: วัดพระศรีรัตนมหาธาตุ; "Temple of Great Jewelled Reliquary"), also colloquially referred to as Wat Yai (Thai: วัดใหญ่; "Big Temple"), is a Buddhist temple (wat) in Phitsanulok Province, Thailand, where it is located on the bank of the Nan River near Naresuan Bridge.