Citrus aurantium var. amara L., commonly known as ‘bitter orange’ or ‘sour orange’, of the familyRutaceae, has traditionally been used in the treatment of various ailments, and it possessesdifferent types of pharmacological properties. As a part of our on-going studies on the plantsfrom the Iranian flora, the extract of C. aurantium var. amara has been studied for its weight lossproperties using the mice model. While the Sep-Pak fraction, 20% methanol (MeOH) in water, ofthe hydro-methanolic extract of the peels of C. aurantium var. amara fruits, when injectedintraperitoneal (i.p.) at a dose of 10 mg/kg, significantly decreased the level of weight gain of themice in comparison with control the group (P < 0.01), the Sep-Pak fraction 80% MeOH in waterdecreased the initial weight of mice by 0.44% in six weeks. The administration of the total extract(10 and 20 mg/kg, i.p.), and the Sep-Pak fractions, 40% and 60% MeOH in water (10 mg/kg, i.p.)did not show any significant change of weight of the test mice. Of the two active fractions, the80% MeOH in water fraction did not show any noticeable adverse effects on mice, and wastherefore analysed by reversed-phase preparative high performance liquid chromatographyresulting in the isolation and identification of four major components, two coumarins, meranzinhydrate (1) and bergamottin (2), and two flavonoids, xanthomicrol 5,4’-di-methyl ether(tangeritin, 3) and hymenoxin 5,7-di-methyl ether (nobiletin, 4).