Phenolic compounds are one of the most abundant metabolites of plants. These compounds enter the aquatic ecosystems through different ways and consequently threat aquatic animal health as well as human life. In this project, the effect of different concentrations of water-borne genistein flavonoid on hematological parameters, including the number of red blood cells (RBC), hemoglobin concentration (Hb), percentage of hematocrit (Hct), mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC) and differential count of white blood cell were studied in common carp weighing 52-82 g. In this study, 5 different treatments of genistein, including 14.8, 28.8, 65.0, 127.3, 223.6 µg/l and a control group were considered in a period of 30 days. At the end of experiment, 7 fish from each treatment were randomly selected and blood samples were then withdrawn. The results showed no significant changes in all measured parameters as compared with the control group. Therefore, the tested concentrations of genistein in the present study could not cause deleterious effects on common carp hematopoiesis. This indicates that phenolic compounds in current conditions did not have any toxic effects on common carp.