Although carotenoid is one of the typical pigments in Staphylococcus aureus, its properties and physiological role have not been well characterized. This paper examined carotenoid of S. aureus in regard to (1) factors affecting its production. (2) chemical properties and (3) its effect on liposomal permeability. (1) Carotenoid content increased during the late logarithmic growth phase. Production was potently accelerated by the addition of 10% NaCl (10 fold), 2% glycerin (10 fold) and 1% glycerolmonoacetate (250 fold). Oxygen was necessary but visible light did not effect the production. (2) The major component of carotenoid was C(30)Diaponeurosporenoic acid methyl ester. Minor components were Diaponeurosporene, Diapo-∫-carotene, Diapolycopenoic acid methyl ester, Diaponeurosporene ester and a hydroxyl derivative of Diaponeurosporene. Staphylococcal carotenoids were all C(30). (3) The addition of carotenoid to liposomes (made of staphylococcal phospholipids) increased the permeability for glycerol and glucose. This indicates that production of carotenoid may be an adaptational response of the bacteria.