The genus Chaetoceros, is known for its abundance and diversity among the planktonic diatoms. Diatoms have long been used in aquaculture, especially as food for bivalves and juvenile gastropods. The general morphology and ultra-structural characters are presented for each species with special emphasis on the distinctive features with respect to species. The diversity and distribution of Chaetoceros (Bacillariophyceae) were studied at monthly intervals, throughout the experimental period (2018-2019) in the Nador Lagoon. A total of 24 Chaetoceros species were identified by inverted light microscopy. The highest recorded abundance of Chaetoceros species was 29320 cell/L, whereas Chaetoceros compressus (16000cell/L), Chaetoceros danicus (7200cell/L) and Chaetoceros descipiens(4120 cell/L) showed the highest dominance. The present work was constructed to determine the distribution of Chaetoceros at the lagoon of Nador in relation to the physicochemical parameters of the environment.