Ordovician nautiloids of central and southern Thailand can be grouped into five broad assemblages. 1, The middle Ibexian fauna of indeterminate endocerids from Tarutao Island. 2, Hardmanoceras chrysanthimum (Kobayashi) of the upper Ibexian age strata on Tarutao Island. 3, The upper Ibexian Manchuroceras nakamense sp. nov. from Ron Phibum, southern Thailand. 4, Wutinoceras sp., Chaohuceras? sp. of lower to middle Whiterockian age strata from Satun Province. 5, Wutinoceras sp., Armenoceras chediforme Kobayashi and Georgina sp. of lower-middle Whiterockian age strata from Kanchanaburi, central Thailand. All of these genera occur in Australia and China.--Modified journal abstract.