Acetaminophen (APAP) poisoning is the most common drug intoxication, which often leads to acute liver failure (ALF). In this study, the effects of different doses of APAP on aminotransferases (AST and ALT) and liver pathological lesions were assessed in young rats. 32 male albino Wistar rats were randomly selected and divided into eight groups. In case groups, three groups after one hour, and 3 groups after three hours were sampled and sacrificed after intraperitoneal injection of 70, 150 and 300 mg/Kg.bw APAP. The variances of necropsy and macroscopic features were recorded after fixation in 10% formalin and staining with hematoxylin and eosin. There was no pathological change in the one or three hours at 75 mg/kg. The 150 mg/kg dose caused mild hyperemia and edema of the portal areas and mild infiltration of inflammatory cells at both one hour and three hours time points. Centrilobular necrosis was mild at 300 mg/kg after one and three hours, and hepatocellular necrosis was sporadically and sligthly elavated for this dose after one hour. Based on multivariate variance analysis test (MANOVA), both dose and time exerted significant effects on ALT and AST activities in the case groups at the first and third hours (P < 0.05). Due to the ability to induce a protective system against acetaminophen toxicity, ALT plasma level evaluation in the early hours will be more helpful than measuring AST level.