The freshwater snail Lanistes carinatus was tested as bioindicator to assess water quality and identify exposure to oil contaminants. L. carinatus was chronically exposed to crude oil at intervals of 24 hours, 15 days and 30 days. The LC50 of crude oil for L. carinatus was 700 ppm. HPLC analysis of 16 polycyclic aromatic hydrocarbons (PAHs) in the flesh demonstrated that PAHs accumulation in the treated snails was fluctuated with time. The accumulation is due to their biotransformation process during metabolism. The histopathological observations of the gills and mantle of L. carinatus showed pronounced alterations at 24 hours and proliferated at the day 15 but showed a further decline at the day 30 of exposure. These findings seem to be time related and were classified as reversible and irreversible changes. Accordingly, it can be concluded that L. carinatusis a typical bioindicator for crude oil pollution.