Fungi are considered one of the pathogen infected in fish. The study was carried out to observe the histopathological changes in fish infected Fusarium sp. A total of 54 fish samples was collected for fungal identification and histological. The colonies is round, light red backside and frontside, the hyphaes grows closely on PDA. Other colonies is round, yellow in backside and the front is white smooth similar as cotton wool. Results of histology determined that tissues of gill, muscle, liver, kidneys does not present spores or hyphae of Fusarium sp. but there are changes in the cell structures. The dense presence of spores and hyphae in sinus of swim bladder.