Dimethoate is an organophosphorus insecticide and acaricide used for the control of a wide range of insects, including houseflies and mites, on a variety of fruits, vegetables, field and forestry crops. The aim of the current study was to evaluate the subchronic toxicity of orally administered dimethoate in Wistar albino rats, based on the histopathological and biochemical findings in the liver. The animals of the exposed groups were fed with laboratory chow combined with 2, 8 or 20 mg/kg body weight/day dimethoate for 90 consecutive days under controlled laboratory conditions. At the end of the experiment, body weight gain, absolute and relative liver weights, liver cholinesterase activities and total protein levels were determined. Histopathological changes in the liver were also determined using a light microscope. Results showed that there were decreases in relative liver weights of exposed rats. Although liver total protein levels were significantly increased, liver cholinesterase activities were decreased in all exposed groups. Dimethoate caused dose-related histopathological changes such as mononuclear cell infiltration, congestion, an enlargement of the veins and sinusoids, hepatocellular damage, necrotic changes, an increase in the number of Kupffer cells, cytoplasmic vacuolization and degeneration in nuclei in the liver of exposed rats. These effects did not vary between the sexes.