This study was carried out to detect the diversity of ciliates inhabiting Damietta branch of the Nile in a sector extending between Benha (Kalubeyia province) and Meet-Badr Hallawa (Dakahleyia province). A total of 38 genera ( 51 species) belonging to eight orders of the ciliate protozoans were identified. Five of these genera were recorded for the first time in that part of the Nile namely : Spathidium, Didinium, Dileptus, Saprodinium and Discomorphella. The most common orders were Hymenostomatida, Gymnostomatida, Hypotrichida, Trichostomatida and Peritrichida followed by the least
common ones: Heterotrichida, Oligotrichida and Odontostomatida. Regarding the ratio between pelagic and benthic ciliates, their percentage values lie within two ranges: the first one was narrow (7.7 - 8.6%) during the period Nov96-Feb97, while the second was wider (9.5-15.4%) during a period extending between March97 and Oct97.
It was also proved that both the ciliate population densities and the organic matter were more or less highest in Benha Nile water and lowest in Meet-Badr Hallawa water throughout the whole studying period. This might be referred to the different human activities in these locations. The values of these two parameters were found to be highest during Sept. 1996 and declined till lowest levels on Feb97 and then they began to reincrease from March97 till Aug97. Both
parameters were found to be correlated and showed high level of statistical significance.