The prevalence and pathological effects of the trematodes in liver and gallbladder of the indigenous ducks in Bangladesh were investigated during the period from July 2003 to June 2004. Out of 300 ducks examined, 208 (69.33%) ducks were infected with one or more species of avian liver flukes. The liver fluke species, recovered from the liver and gallbladder were: Metorchis orientalis (55.33%), Amphimerus anatis (54.33%), Amphimerus lancea (12.00%) and Amphimerus caudalitestis (1.00%). The highest prevalence was recorded in monsoon (91.30%) followed by winter (76.51%) and summer (49.52%). Similarly, the parasitic load was relatively higher in monsoon (23.10±3.10) followed by winter (18.76±2.98) and summer (08.99±2.95). The prevalence of the trematodes was significantly (P<0.01) higher in adult ducks (82.61%) than in the young ducks (25.71%). The mean parasitic density was also higher in adult ducks (25.24±3.99) of > 6 months age than in the young ducks (06.91±1.39) of <6 months age. Almost similar rate of infection was recorded in male (70.71%) and female (68.13%) ducks with an average parasitic burden of 26.41±3.54 and 24.92±2.96 respectively. In most cases, the parasitized liver was slightly atrophied characterized by the smaller size with shrinkage or wrinkling of the liver capsule. The edges or borders of the livers were sharp along with tiny white necrotic foci in some cases. On cut surface, the parasites were found in the bile ducts but no calcification was detected. Grossly, gallbladder was apparently normal containing adult parasites in it. Histopathologically, cross-section of parasites with their eggs and cellular debris were found within the bile ducts. Desquamation of the bile duct epithelium was observed but in some cases, the bile duct epithelium was hyperplastic in nature. Microabscesses with infiltration of lymphocytes, macrophages and polymorphonuclear cells predominantly neutrophils were revealed in the hepatic lobules. Proliferation of the fibroblasts occurred around the bile ducts. But in advanced cases, extensive fibrosis observed which extended from the portal triads to the adjacent hepatic lobules resulting disorganization of the normal hepatic architecture leading to cirrhosis. In severe cases, the normal structures of the bile ducts were almost obliterated by the extensive proliferation of the fibroblasts converting it into a fibrous tube. This study suggests that the avian liver flukes of the indigenous ducks of all ages and sexes may be a major problem.