Justicia insularis leaves widely used in African traditional medicine for the management of malaria, pains, diabetes, convulsion and bacterial infections was screened for its acute and sub-acute effects in Wistar rats. In acute toxic test, the leaf extract was orally administered to rats up to 5 g/kg in different doses. This was followed by observing the animals for signs of toxicity and mortality for 7 day. In sub-acute toxicity study, the rats were orally treated daily with J. insularis ethanol extract at doses of 200 mg/kg, 400 mg/kg and 600 mg/kg for 21 days. The rats used for control were given distilled water. All animals were weighed at 7 day intervals all through the study and the haematological, biochemical parameters and vital organs were all determined, at the end of the study. J. insularis ethanol leaf extract was practically non-toxic showing no mortality and visible signs of toxicity on acute exposure. The extract showed significant increase in the body weight of rats given 400 mg/kg and 600 mg/kg compared to control. The leaf extract showed significant increase in haematological indices, but there was no alteration in biochemical indices, and the vital organs as well. Findings in this study revealed that J. insularis was safe when orally administered, while we suggest further investigation to ascertain its effect on long-term administration.