The two main pregastric compartiments of ruminants: rumen and reticulum work as anaerobic fermenter which allows them to use energetic and nitrogen substrates which are indigestible by monograstric animals. They have a major importance in this fermenter, also these microbes : bacteria, protozoa and fungi, on the degradation of cell-wall carbohydrates: cellulose, hemicelluloses, pectic substances, on nitrogen digestion and finally on the utilisation of the major minerals and trace elements. The objective of this study is to identify and quantify the protozoa populations in the rumen of Algerian bovines local breed, adult animals living in a relatively humid climate, basic ration based on straw and pastures during hot days. Whereas in cold weather rations are based on straw, cereals and grass forage. Usually not 2 to 5 × 10 6 ml of rumen containing organisms however, under certain feeding conditions, they represent at least 50 % of the rumen microbial biomass. Due to the difficulties in cultivate in vitro, their role and their metabolism are less known than those of bacteria. Ciliated protozoa are capable of transforming a large number of food and bacterial constituents in metabolites and cellular compounds which will then be used by the host animal. The importance of these activities is however still very controversial since in the absence of protozoa in the rumen, Isolation carried out on rumen fluid sampled of 20 cows. Rumen fluid was diluted in formaldehyde 10 % solution, and distributed in Sedgewick Rafter chamber. Then observed in optical microscope using Lugol's iodine coloration. Classified in three genders according to size. 11 different genders were identified; a considerable population of rumen protozoa was identified and classified for first time on Algerian local breed (Atlas).