PURPOSE: To provide the subject excellent preparation active to the therapy of hypertension without affecting human bodies and having low toxicity and no side effect by containing a complex polysaccharide comprising L-arabinose, D-ribose and D-glucose as main constituting saccharides as an active ingredient.

CONSTITUTION: An antihypertensive agent contains as an active ingredient a complex polysaccharide having a molecular weight of approximately 40000, containing L-arabinose, D-ribose and D-glucose as main constituting saccharides and further containing D-mannose and D-sorbose or an extract containing the complex polysaccharide. The complex polysaccharide is prepared by extracting coase tea or green tea with water or by extracting the water extract with an organic solvent. The water extraction is performed by dispersing the coase tea or green tea in water at 0-80°C, stirring the dispersion for approximately 10min and subsequently filtering the stirred dispersion. The antihypertensive agent is employed after the active ingredient or a mixture thereof with any other active ingredient is shaped together with a carrier into a preparation.