In the present study, freshwater fish Oreochromis mossambicus were exposed to sub lethal concentrations (120,150 and 180 ppm) of Aluminium oxide nanoparticles (Al₂O₃ NP_s) for 96 h. Histological abnormalities were not observed in the organs of control fishes whereas severe damages and extensive architectural loss was found in the brain, gill, intestine, kidney and muscle tissues of treated fishes with more pronounced effects in 180 ppm.The results showed that the acute exposure to Al₂O₃NP_s altered the histoarchitecture in various fish tissues.