In this study, a mixture of a suitable chalcone and p-hydrazinobenzenesulfonamide hydrochloride in 1:1.1 mol ratio in ethanol (25 ml) in the presence of glacial acetic acid (0.05 ml) was refluxed for synthesis of 4-(3-(4-Bromophenyl)-5-(2,4-dimethoxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl) benzenesulfonamide, B4, for 7h at first experiment. Effects of B4 on antioxidant enzymes of gill and liver, and changes in hematological parameters were determined in rainbow trout. For this purpose, rainbow trout alevins were exposed to 0, 0.25, 0.5, 1 and 2.5 mg/L of B4 and 1 ml of DMSO for 96 hours. Blood samples were collected for hematological analyzes and mortalities were recorded daily. Exposure to B4 caused significant changes in antioxidant enzymes of gill and liver of alevins (p<0,05). Catalase, superoxide dismutase (SOD) and glutathione peroxidase activities were decreased, while MDA values increased significantly (p<0.05) in gill and liver of fish compared to control group. SOD activity was time dependent; it decreased initially, but then take increased. WBC, MCV, MCH and MCHC levels increased, while RBC Hb, Htc and PLT levels decreased with increasing dose from 0.25 to 2.5 mg/L of B4 (p<0.05) compared to control. There were no differences between control and DMSO group (p>0.05) with respect to all tested properties. It is suggested that B4 should be investigated further for possible usage in aquaculture industry to produce healthy fish.