Brown trout, Salmo trutta fario, has a wide range of distribution in the north of Iran and in Karaj, Lighvanchai and Karun Rivers, but there is no report about its feeding behavior in some water resources including the Lar Natural Park. In order to study feeding behavior of this fish during spawning season, a survey was carried out in the rivers of Elarm, Aab-Sefid, Kamardasht and Delichayi in fall 2008. A total of 140 individuals of brown trout were caught by cast net and electro fishing. Mean weight and length of the samples were 130?79.5 g and 216.9?39 mm, respectively. The age of fish was 2 to 6 years and mean age was 3.02?1.3. The mean relative gut length (RLG) of samples was 0.86?1. It was found that brown trout fed on various preys (32 animal groups), that Chironomidae (88.6%), Simulidae (60%), Baetidae (51.4%) and Tipulidae (50%) have had the most frequency in the gut of brown trout. The proportion of food consumed by trout was Diptera 91.5% (Chironomidae pupa and larvae 85.8%), Coleoptera 6.4% and others 2.1%. Cannibalism was seen scarcely. In conclusion, brown trout consumes a wide range of food items in its spawning season. Therefore, it can be classified as euryphagous and carnivaorous.