Abstract: The five common intestinal flagellates in laboratory rats,Retortamonas sp.，Penta tri-chomonas hominis,Tetratrichamonas microti,Tritrichomoyias minuta and Tririchomonas muris were observed under light microscope and electron microscope. The movement,the shape and the organelle systems such as flagellum,costa,undulating membrance，axostyle and nucleus of each species under the light microscope were described.On the basis of morphology,Pentatrichomonas hominis and Tetratrichomonas microtiwere classified into hominis-type flagellate；Tritrichomonas minuta and Tririchomonas muris were classified into muris-type flagellate.Through the scanning electron microscope，it was observed that three flagella of Pentatrichomonas hominis were arisen from three different anterior parts of the trophozoite，that differed from the traditional morphological acknowle-dgement.

Key words: Rat, Intestinal flagellate, Light microscope, Scanning electron microscope, Morphological observation