In this study, the feeding habits of the Isfahan chab, Petroleuciscus esfahani and nase fish, Chondrostoma regium were investigated by collection of 200 specimen of each species (male, female and immature), from Zayandeh Roud River in Chahar - mahal and Bakhtiari province. Seasonal sampling was carried out during May 2013 to February 2014 for both fish and benthic organisms. In this research, the benthic organisms Viz. Insecta, Hirudinea, Oligochaeta, Lamellibranchiata, Gastropoda, Arachnida and Crustacea, 11 orders and 33 families were identified that the major taxons were belong to aquatic insect larvae. The total range of length in Isfahan chab was 43.2 to 170.5mm (127.1±8.2)(mean±standard deviation) and weight ranged 1.1 to 56.5g (25.4±1.6), correspondingly, the total range length of nase fish was 52.7 to 191.8mm (145.5±11.2), and weight ranged 1.6 to 96.3g (37.5±2.5). Results on examined gut contents showed for Isfahan chab and nase fish Vacuity Index 11.5% and 24%, respectively. The vacuity indices showed no significant differences (P?0.05) among seasonal sampling, with a maximum in autumn in both species and minimum in winter and summer for Isfahan chab and nase fish, respectively. Relative length of gut (RLG) in two species were 0.73±0.08 and 1.36±0.24, respectively with not any significant difference among age groups during all over the year (P?0.05). In the gut contents of Isfahan chab and nase fish, generally, identified 29 different prey items including 7 main Key words: Gut contents, Feeding habits, Petroleuciscus esfahani , Chondrostoma regium
