Cajanus cajan (L.) Millsp. (Fabaceae, local name: orhor, English name: pigeon pea) is widely cultivated in Bangladesh for its edible seeds. The leaves are also consumed during times of food scarcity. In the folk medicinal system of Bangladesh, the leaves and stems of the plant are predominantly used for treatment of jaundice and diabetes. The objective of the present study was to evaluate the antihyperglycemic and cytotoxic potential of methanol extract of leaves and roots of the plant. Antihyperglycemic activity was studied by oral glucose tolerance tests in glucose-loaded Swiss albino mice. The methanol extract of leaves showed dose- dependent and significant reductions of serum glucose levels in mice. At doses of 200 and 400 mg leaf extract/kg body weight, the reductions in glucose levels were comparable to that of the standard antihyperglycemic drug, glibenclamide, administered at a dose of 10 mg/kg body weight. In contrast, the methanol extract of roots showed a dose-dependent increase in serum glucose levels, which was statistically significant at the highest dose of 400 mg extract/kg body weight. The cytotoxic potential of methanol extracts of leaves and roots were measured with the brine shrimp lethality bioassay. Both leaf and root extracts showed a high degree of toxicity to brine shrimp with LC50 values, respectively, of 0.0264 and 1.849 mg/ml. The results obtained with antihyperglycemic tests with leaves of the plant validate its folk medicinal use for diabetes. The brine shrimp lethality assay results suggest that the plant can be a promising source of anti- cancer compounds.