The present study was designed to determine the preliminary oral toxicity profile of the aqueous extract of bark of Helicteres isora L. (HIL) in rats and its active chemical constituents by way of phytochemistry. The acute oral toxicity study was conducted using limit dose test of up and down procedure according to the OECD/OCDE Test Guidelines on Acute Oral Toxicity (AOT425statPgm, version: 1.0) at a limit dose of 2000 mg/kg/p.o. Repeat dose oral toxicity studies were conducted by daily oral dosing of 500 mg kg-1 b.w of HIL dissolved in 1 mL of 0.9% saline and 1 mL of 0.9% saline to rats in the test and control groups, respectively, for 28 days. On day 29, blood samples for bioassays were collected by cardiac puncture under chloroform anesthesia. The phytochemical analysis was conducted using standard procedures. The LD50 estimate of the extract was calculated to be greater than 2000 mg/kg/p.o. The extract caused a significant (p<0.05) decrease in weight gain, differential eosinophil count and increase in serum creatinine but did not affect the organ weights, other serum electrolytes (Na+, K+, HCO3), liver enzymes and other hematological indices in test rats. Its phytochemical analysis showed it contains saponins, flavonoids, alkaloids, tannins, phlobatannins, glycosides, reducing sugars and anthraquinones. These results show that the aqueous extract of Helicteres isora is relatively safe toxicologically when administered orally. Thus, its use in folkloric medicine as an oral antidiabetic is relatively safe when used over the tested period.