The feeding habits and diet composition of the stream dwelling resident brown trout Salmo trutta in the upper streams of River Ceyhan and River Euphrates were investigated by examining the stomach contents of 611 specimens collected from May 2000 to April 2001. Analysis of monthly variations of stomach fullness indicated that feeding intensity was higher between February and June than that for the spawning season that covered the period from November to January. A total of 42 prey taxa representing Coleoptera, Trichoptera, Ephemeroptera, Plecoptera, Malacostraca, Diptera, Araneidae, Odonata, Gastropoda, Acridae, Acarii, Heteroptera, fish and fish egg was identified in the diet. The index of relative importance (IRI%) revealed that five food items together constituted more than 90% of the diet, with the most important being Gammarus sp. (49.72%), Hydropsychidae (14.61%). an unidentified dipteran species (9.21%), Nemoura sp. (8.98%) and Isoperla sp. (6.90%). The Overlap Index (OI) values indicated that the resident brown trout in the Stream Aksu, Sogutlu and Hurman differed in terms of their diet compositions, compared to the trout in other streams. The most important food item varied among the size classes of the brown trout, being Rhithrogena sp., Nemoura sp., Gammarus sp. and fish for the classes of trout with 40-80 mm, 81-120 mm, 121-280 mm, and > 320 mm fork length, respectively. Diet composition of brown trout < 80 mm in length and > 240 mm in length was different from the other length groups (OI < 0.7). High value overlap index was observed between female and male (OI = 0.989), while no significant dietary overlap was evident between immature and mature individuals (OI = 0.465 and OI = 0.472).