Since 1956. the Institute of Oceanology, Academia Sinica, has condueted several scientific surveys of the Xisha Islands, emphasis being placed on faunal and floral studies. the results of which have been published in scores of papers. The present paper gives the preliminary results of an ecological survey of the reef flats of the Jinyin Island and the Dongdao Island conducted during May-june in 1975 and of an algal survey conducted during January-april in 1976. The purpose of these two surveys was to have an understanding of the zonation structure of the vertieal distribution, as well as species composition and abundance of the benthic algae and invertebrates of tropical coral reef flats, of the distribution pattern of fishes during ebb tide, and of the life types of coral reef fishes, as a basis for their rational exploitation and utilization.