Abstract: This study was elucidated in order to evaluate the effects of ethanolic leaf extract of Madagascar periwinkle (Catharanthus roseus) (documented for its hypoglycemic effects on experimental animals) on the activities of glucose-6-phosphate dehydrogenase and lactate dehydrogenase on the kidney, liver and pancreas of adult Wistar rats. Thirty-two rats (of the first filial generation) of both sexes (Albino, Wistar) were used. Animals weighed 214-232 g and were about 7-13 weeks old. The animals were divided into four groups designated as A, B, C and D of eight animals in each. Groups A, B and C were administered with 400 mg kg-1, 300 mg kg-1 and 200 mg kg-1 b.wt. of the plant extract respectively while the control group was administered with equal volume of phosphate buffered saline orally for 21 days. At termination of study, it was observed that there was significant increase in glucose-6-phosphate dehydrogenase and significant decrease in lactate dehydrogenase enzyme activities in the administered groups. The results obtained from this study suggested that the leaf extract of Madagascar periwinkle (Catharanthus roseus) consumed for its hypoglycemic effects, alters carbohydrate metabolism in the kidney, liver and pancreas and has no deleterious effect on the organs of study in Wistar rats. Further studies should be done in order to know if such effects seen in Wistar rats may by extension be seen in man.