The majority of fungicides, including captan, used in gardens and farms are washed into the aquatic environments. These compounds can lead to extensive side effects on the inhabitants living in that exposed area. In this research, toxicity of captan on fingerling grass carps (3-5 g) was studied. Based on the results, captan was categorized as an acute toxin with LC5096h and MAC values of 0.9 and 0.09 mg/ml, respectively. This toxin damaged severely the gills and liver of fishes and the toxic severity increased in higher doses of the toxin. Furthermore, hematochemical studies showed significant drops in all red blood cell criteria, except for MCH (mean corpuscular haemoglobin) and MCV (mean corpuscular volume). Besides, captan decreased significantly the total immunoglobulin and white blood cell counts, except for monocytes and neutrophils. As a conclusion, captan causes detrimental effects on several tissues of Ctenopharyngodon idella, and therefore limited utilisation of this fungicide is recommended strongly.