The present thesis seeks to document the diversity of the flagellates in some sediments of the Oslofjord. The analysis of these sediments lasted from January 2005 until June of the same year. The sand samples were collected from the surf zone, that is, the wave zone, of two beaches: Huk, in the Bygdøy peninsula, and Hulvika, south to the city of Oslo. Huk was sampled seven times, whereas, Hulvika six times. Along with the sediment samples, three variables were measured: temperature, salinity and pH.Samples were immediately transferred into plastic petri dishes and coverslip put on top. These coverslips were examined in the light microscope for identification of species. Besides, some samples were processed for extracting the organisms by means of the so-called ice-method. The water extracted by this method would be employed for the preparations for scanning electron microscopy.All in all, 85 different flagellate taxa were found in the two localities, 71 of which were identified down to species level in the light microscope. Of the total taxa 22 were autotrophs, while 63 were heterotrophic species. In general, the autotrophs began to increase in species diversity and abundance with the arrival of spring and summertime. The Huk location showed a higher diversity in euglenoids than Hulvika. Finer sand prooved to contain more species of some dinoflagellate genera as compared to coarser sand.As for the variables measured, temperature followed an increase with season, while salinity showed an irregular pattern. No correlation could be demonstrated between the occurrence of species, both abundance and diversity, with the environmental variables measured. Most probably, increase of light due to seasonality and consequently a higher oxygen concentration, were the causes for the succession of species from low abundance and heterotrophic specimens to higher abundance and autotrophic specimens.