Epizootic ulcerative syndrome (EUS) is a dreadful disease of several aquatic animals including mrigal (Cirrhinus mrigala Ham.). Prevention of the disease with the help of chemical compo-unds may prove harmful for the fish as well as the end consumer. Now-a-days the use of pro-biotics has become firmly established due to their beneficial effects at the nutritional as well as therapeutic levels. Therefore, research efforts have been concentrated on optimizing production with eco-friendly alternatives to the therapeutic use of antimicrobials. Commercially available probiotics were used for controlling this disease in mrigal in the present study. The effect of probiotic on four haemotogical parameters viz. amount of haemoglobin (Hb), hemocrit / pac-ked cell volume (PCV), total erythrocyte count (TEC), and total leucocytes count (TLC) were studied over a period of eight weeks. The level of these parameters decreased significantly in the blood of fish treated with pathogenic bacteria. The fish administrated with probiotics showed significant increase in the hematological parameters thus contributing towards overall health of the fish.