This paper describes a new actinocerid cephalopod fauna from the western part of the Shan Plateau in Myanmar (Sibumasu Block), and discusses its significance. The cephalopod fossils are preserved in shallow marine limestones of the Wunbye Formation (Pindaya Group) and its equivalent strata. The fauna consists of Ordosoceras theini sp. nov. (Floian or Dapingian, late Early or early Middle Ordovician age), Armenoceras myanmarense sp. nov. (Darriwilian, late Middle Ordovician), Paratunkuskoceras sp. (Darriwilian), and Wutinoceras moeseini (Floian, late Early Ordovician). The presence of Ordosoceras, which was previously known only in the North China Block, and specific characters in the actinocerid fauna of Sibumasu indicate a strong linkage with that of North China during Early—Middle Ordovician time; in contrast, Sibumasu's affinity to the coeval Australian fauna is less definable. It is possible that an actinocerid faunal exchange took place between North China and Sibumasu over the shelf sea environment open to the Prototethys Ocean but this did not happen to the inland seas of Australian Gondwana during the period.