Length‐weight relationships (LWR) for seven species from the Karun River system in Iran were provided. These species include Alburnus doriae, Alburnus sellal, Barbus karunensis, Capoeta coadi, Squalius berak, Turcinoemacheilus saadii and Rhinogobius lindberg. Fishes were collected in November and December 2018 and LWR is based on total length and weight of 2867 specimens calculated by equation W= aLb . The b value ranged from 2.92 to 3.25 and r2 from 0.94 to 0.99. The length and weight range is presented for each species collected in the Karun River Basin.