Thumbergia laurifolia Lindl. or rang chuet, is a medicinal plant that is used for the treatment of poisoning with toxic substances. However, the toxicological data for this plant are not complete. Therefore, a chronic toxicity study of rang chuet extract (TLE) was undertaken in six groups of Wistar rats. The control group(group 1) was given 10 ml/kg of distilled water per day orally. The five experimental groups (groups 2-6) were orally administered TLE at doses of 20, 200, 1,000, 2,000 and 2,000 mg/kg/day for six months, respectively, which were equivalent to 1, 10, 50, and 100 times the therapeutic dose. Group 6 (2000R) was added to the study recovery group after 14 days of TLE discontinuation. The results revealed that TLE did not affect the body weight, food consumption, behavior or general health of the animals. TLE did not produce cumulative toxic signs and fatal effects. Male rats receiving TLE at the dose of 2,000 mg/kg/day and the 2000R group had a significant decrease in RBCs, including a significant difference in red cell indices, but these were within the normal range. Female rats receiving TLE at doses of 1,000 and 2,000 mg/kg/day showed significant increases in WBCs. Both sexes of the rats treated with 2,000 mg/kg of TLE had a significant increase in bilirubin levels; however, these were within the normal range. TLE did not produce any histological alterations of the visceral organs in any group of rats. However, the results suggest that hematological and clinical chemistry values should be monitored during prolonged use of TLE.