Diverse and significant well-preserved radiolarians were obtained from ribbon-bedded chert in an area to the north of Chiang Dao city, Chiang Mai, northern Thailand. The area is mainly composed of an accretionary complex, which is recently considered as a key part of a newly described suture zone in the Southeast Asian region. Devonian radiolarian-bearing cherts are exposed within this area. These cherts contain identical radiolarian faunas, which include nine families and forty-three species belonging to thirteen genera. Among these faunas, Entactinaria are dominant. Three new species, Trilonche chiangdaoensis, Trilonche dihelicis and Trilonche vachardi, are erected and about thirty species, which have never been reported from Thailand, are also present. The Trilonche minax (lower Frasnian) radiolarian assemblage from Australia is recognized in the area. The radiolarian faunas are systematically described and relationships between them and fauna from adjacent radiolarian provinces are discussed. These cherts with their radiolarian faunas are evidence for the presence of a wide paleo-ocean once existed between Shan-Thai and Indochina continental terranes.