In this study, gastric contents of the medusa Rhizostoma pulmo distributed along the Samsun coast of the Black Sea were investigatedbetween August 2008 and January 2010. Moreover, the relationship between the umbrella diameter and prey selectivity was determined.Captured R. pulmo individuals during the sampling period varied from 14.5 to 42.5 cm in umbrella diameter. The largest umbrella diameterwas observed in October in both periods of the present study. Gastric contents of total 231 R. pulmo individuals have been gathered duringthe sampling period from all stations. 31 taxa, 10 larvae, 2 nauplii and fish and Copepod eggs from 11 phyla have been identified in the gastriccontents of R. pulmo individuals. It has been detected that, feeding choices of R. pulmo individuals have differentiated and their food counthas increased due to increasing umbrella diameter (according to Spearman rank correlation, r=0.70; p<0.05). According to the gastric contentanalyses, the feeding dietary of this species predominantly consists of copepods and dinoflagellates. It has been observed that taxa belongingto Crustaceans (59 %; Copepods 45.9 %) and Dinoflagellates (15.4 %) were densely present in the gastric contents gathered from R. pulmoindividuals. The Phylum Ciliophora was another abundantly observed group in the gastric content of R. pulmo, with a 7.2 % representationrate. It was determined that jellyfish have a wide range of nutrition from phytoplankton to fish eggs. The sort of prey and amount of nutritionin stomach contents increased in parallel with the umbrella size. It is concluded that R. pulmo has important effects on the pelagic zone of theBlack Sea ecosystem.