In this study, the effects of coriander (Coriandrum sativum) on reducing oxidative stress in Cyprinus carpio were assessed. The biological material represented by ornamental carp juveniles (Cyprinus carpio - var. koi), with homogeneous sizes and weights, was distributed in a recirculating growth system in three experimental variants: variant A1 (control) in which the fish were fed with unadditive feed, variant A2 - in which the fish were fed with feed supplemented with 1% coriander and variant A3 - in which the fish were fed with feed supplemented with 3% coriander. Coriander powder was obtained by grinding the seeds and then incorporated into the commercial Coppens feed with the help of gelatin. The experiment lasted for 47 days. The assessment of oxidative stress was carried out through indirect methods represented by the analysis of hematological parameters, which indicated the general state of health and physiological reactions to stress. Thus, the following hematological parameters were determined: hematocrit (Ht), hemoglobin level (Hb), mean red blood cell volume (MRC), mean red blood cell hemoglobin (MRC), mean red blood cell hemoglobin concentration (MRC), total serum proteins and glucose. The results of this experiment, from a hematological point of view, where the values of blood indices were placed in optimal ranges characteristic of the species, in contrast to the high values of nitrates and ammonium, as well as phosphates, explain the antioxidant role of coriander in reducing oxidative stress.