Cardiovascular complications are a major cause of morbidity and mortality in patients with diabetes, obesity and the metabolic syndrome. Recently, there has been an increasing interest in tea as a protective agent against CVD. Here, we compared the modulatory effects of two different doses (50 and 100 mg/kg body weight given orally for 28 consecutive days) of black tea aqueous extract (BTE, rich in theaflavins and thearubigins) and green tea aqueous extract (GTE, rich in catechins) on experimentally induced hyperglycaemia, hyperlipidaemia and liver dysfunction by alloxan (which destroys pancreatic β-cells and induces type 1 diabetes) and a cholesterol-rich diet (which induces obesity and type 2 diabetes) in male Wistar albino rats. Both tea extracts significantly alleviated most signs of the metabolic syndrome including hyperglycaemia (resulting from type 1 and 2 diabetes), dyslipidaemia and impairment of liver functions induced by alloxan or the cholesterol-rich diet in the animals. Also, the tea extracts significantly modulated both the severe decrease and increase in body weight induced by alloxan and the high-cholesterol diet, respectively. The modulatory effects obtained here were partial or complete, but significant and dose dependent, and slightly more in GTE in most cases. No harmful effects were detected for tea consumption on all parameters measured, except that the high dose of both tea extracts significantly decreased the spleen weight:body weight ratio and induced lymphopenia. The present study supports the hypothesis that both black and green teas may have beneficial effects against the risks of the metabolic syndrome and CVD as shown in rat models of human obesity and diabetes.