The aim of the present study was to evaluate the sub-acute oral toxicity of acetaminophen in Sprague Dawley (SD) rats at 250 to 1000 mg/kg body weight (b.wt.). The following observations were noticed during the study. No mortality in male and female rats, at and up to the dose of 1000 mg/kg b.wt. There were abnormal clinical signs observed on female animals at 1000 mg/kg b.wt. dose level. There were no difference in body weight gain and no effect on the daily feed consumption. No toxicologically significant effect on the haematological parameters but liver and kidney related biochemical parameter showed significant difference at 1000 mg/kg b.wt. in females. No toxicologically significant effect on the urinalysis parameters, absolute and relative organ weights and gross pathological alterations; whereas histopathological alterations were observed in female liver at dose level of 1000 mg/kg b.wt. were observed. Based on the findings of this study, the No Observed Adverse Effect Level (NOAEL) of acetaminophen in SD rats, following oral administration at the doses of 250, 500 and 1000 mg/kg on daily basis was found to be 500 mg/kg b.wt.