Persian sturgeon, Acipenser persicus is a native, commercially important and highly steemed fish species in the Caspian Sea. In this study, effects of Nodularin (NODLN), a cyclic pentapeptide hepatotoxin, on liver and gill tissues of A. persicus were studied. Nodularin was produced in high amounts by Nodularia spumigena, a cyanobacterium species during the algal bloom in the Caspian Sea and was accumulated in biota of the Sea. Persian sturgeon were exposed directly to NODLN as prolonged immersion containing N. spumigena in two different doses (1?104 and 1? 108 cells.ml-1) for 24, 48 and 96 hours to examine its histopathological effects on fish liver and gill. Histopathological examinations revealed loss of liver architecture, degeneration of hepatocytes, nuclear pyknosis, karyolysis and finally necrosis of the cells over the time. Observation of gill tissues following immersion in algal cells treatments showed hypertrophy, fusion of secondary lamellae due to proliferation (hyperplasia) of branchial epithelium in low dose and vacuolization of epithelial and pilar cells, tellangiectasis, fusion of secondary and primary lamellae, complete necrosis and sloughing of secondary lamellar epithelium in high dose.