A study conducted with a total 480 sample number of fishes Trichogaster pectoralis (Regan, 1910). All of helminths were identified in to 16 species : 11 species of digene, Clinostomum philippinensis, Clinostomum complanatum, Pothodiplostomum minimum, Nanophyetus sp., Stephanostomum sp., family Echinostomatidae, Gyrodactylus sp. A, Gyrodactylus sp. B, Gyrodactylus sp. C, Gyrodactylus sp. D and Gyrodactylus sp. E; four species of nematode, Strongyloides sp., Camallanus yehi, Camallanus trichogasterae, Contracaecum sp. and one species of Acanthocephala, Pallisentis nagpurensis. The incidence were 70.6%, 6.25%, 0.41%, 9.58%, 0.41%, 0.41%, 1.04%, 2.7%, 0.21%, 0.21%, 0.21%, 22.7%, 0.41%,0.21%, 14.6% and 47.3% respectively. This study is the first report about 11 species of helminths, Clinostomum complanatum, Pothodiplostomum minimum, Stephanostomum sp., Echinostomatidae, Gyrodactylus sp. A, Gyrodactylus sp. B, Gyrodactylus sp. C, Gyrodactylus sp. D, Gyrodactylus sp. E, Strongyloides sp., Camallanus trichogasterae, found in Trichogaster pectoralis (Regan, 1910), Six species are possibly new species, Gyrodactylus sp. A, Gyrodactylus sp. B, Gyrodactylus sp. C, Gyrodactylus sp. D, Gyrodactylus sp. E and Strongyloides sp. Histological studies investigated on six species of helminths with highly infection. It was found that, Clinostomum philippinensis, Clinostomum complanatum and Strongyloides sp. were not pathogenic to be comparable with Pallisentis nagpurensis, Contracaecum sp. and Nanophyetus sp., which caused degeneration of liver, bile duct proliferation, hepatic cell regeneration to compensate pressure atrophy hepatic cell, degeneration of pancreas, finding eosinophils and macrophages near cysts, forming fibrous tissue instead of pressure atrophy hepatic cell. Not only that, Contracaecum sp. had high effect to stomach, it made inflame and chronic infection. Infection of Pallisentis nagpurensis, Contracaecum sp. and Nanophyetus sp. might be main causes to lose economic of Trichogaster pectoralis (Regan, 1910)
