Acetaminophen is used as an analgesic and antipyretic. Due to its relative safety at therapeutic dose, it is frequently used in children and in pregnant women. We evaluated the effect of a dose equivalent to the therapeutic dose of Acetaminophen in undernourished rats; 72 Wistar male rats of 18 weeks of age, with weight between 270 and 280 g, were distributed randomly in four groups: A, normal without food restriction; B, normal without food restriction treated with Acetaminophen (100 mg/kg); C; undernourished by food restriction and D, undernourished by food restriction treated with Acetaminophen (100 mg/kg). The results showed decreasing of body and hepatic weight in undernourished rats and in undernourished treated with Acetaminophen, significant decrease of serum albumin concentration (p < 0.001). It was demonstrated that activity of the enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase significantly decreased (p < 0.001) in the group of undernourished rats treated with Acetaminophen compared with the other groups. We concluded that the Acetaminophen induces hepatic lesions in undernourished rats treated with a single non toxic dose of 100 mg/kg of weight, probably as a consequence of the inherent susceptibility to malnutrition.