Euthalia Rosempona Fruhstorfer is one of the endemic butterflies in Taiwan. We found that hatching larvae feed on Cyclobalanopsis pachytloma (O. Seem) leaves and can completely mature on this plant. This is Ist record of this being a host plant in Taiwan. This Ist paper describes the morphology of egg, larva, and pupa of E. Rosempona Fruhstorfer. We also make some suggestions on butterfly conversation.