The water decoction of leaves of kumis kucing, Orthosiphon aristatus (BL.) MIQ (Lamiaceae) which has been prescribed in Javanese traditional medicine (jamu) for the treatment of hypertension etc., was partitioned into a mixture of chloroform and water. The chloroform-soluble portion showed an inhibitory effect on the contractile responses on rat thoracic aorta smooth muscle stimulated with KCl beforehand, while the water-soluble portion showed no effect. The chloroform-soluble portion was separated to afford a new benzochromene [orthochromene A (7)], two new isopimarane-type diterpenes [orthosiphonone A (10), orthosiphonone B (11)], and two novel migrated pimarane-type diterpenes [neoorthosiphol A (12), neoorthosiphol B (13)], together with eight known compounds (1-6, 8, 9). Among those thirteen substances, it was found that a major constituent in the water decoction of leaves, methylripariochromene A (5), exhibited a continuous decrease in systolic blood pressure after subcutaneous administration in conscious stroke-prone spontaneously hypertensive rats (SHRSP).