In the present study, the aqueous leaf extract of Ocimum tenuiflorum (Linn.) was subjected to toxicity assessment in wistar albino rats at different dose levels of 100, 500 and 1000mg/kg body weight. No major changes in body weight were observed at the end of 30 days of daily oral administration. Biochemical parameters such as the levels of Protein, Urea, Creatinine, Uric acid, Aspartate Transaminase [AST], Alanine Transaminase [ALT], Lactate Dehydrogenase [LDH] in serum were found to be well within the normal limits. The levels of marker enzymes in the vital organs did not show any statistical significance between control and treated groups of animals. Histopathological examination of the major vital organs (liver, heart, kidney, lung and brain) revealed no significant pathological alterations in the treated group of rats. In conclusion, the present study shows that the aqueous leaf extract of Ocimum tenuiflorum is safe and non-toxic at the doses tested.