Length–weight relationships have been determined for two species, Mastacembelus mastacembelus and Glyptothorax silviae. Samples were taken in 2011 from the Cholvar River in western Iran. It is believed that the size range covered is close to a commonly known size range of each species. The length–weight relationship values of b were determined as 2.66 for M. mastacembelus and 3.045 for G. silviae. However these data are based on preserved specimens, and a correction factor for live lengths and weights is still warranted.