The effect of salinity on the distribution of copepoda in the Jiulong Estuary is studied in the present paper. The analysis of the samples collected during February 1983-January 1984 shows that the salinity of the Jiulong Estuary varies from 0.04 at Station E (head of estuary) to 31.7 at Station C (mouth of estuary). The distribution of copepoda is obviously affected by salinity. The results of the investigation show that the number of species, Shannon-Weaver H’ index of diversity, species richness d and species evenness J’ of copepoda increase with increasing salinity. Especially between the Station D and the Station C, being dominated by three predominant species. But, on the other hand, the total number of individuals apears to decrease with increasing salinity. According to the relation of distribution of copepoda with salinity, the copepoda may be divided into five ecological groups, i.e. fresh-water, low-salinity estuarine, meso-salinity estuarine, neritic and oceanic groups. Their horizontal succ The effect of salinity on the distribution of copepoda in the Jiulong Estuary is studied in the present paper. The analysis of the samples collected during February 1983-January 1984 shows that the salinity of the Jiulong Estuary varies from 0.04 at Station E (head of estuary ) to 31.7 at Station C (mouth of estuary). The distribution of copepoda is obviously affected by salinity. The results of the investigation show that the number of species, Shannon-Weaver H ’index of diversity, species richness d and species evenness J Especially coherent to the Station D and the Station C, being dominated by three predominant species. But, on the other hand, the total number of individuals apears to decrease with increasing salinity. According to the relation of distribution of copepoda with salinity, the copepoda may be divided into five ecological groups, ie fresh-water, low-salinity estuarine, meso-salinity estuarine, neritic and oceanic groups. The ir horizontal succ