Six compounds hispidulin-7-glucuronide (1), beta-sitosterol (2), conferyl aldehyde (3), 2 '-hydroxyl-5 '-methyoxybiochanin A (4), and hispidulin-7-O-D-glycoside (5), 6-methoxyluteolin-7-glycoside (6) were isolated from Salvia plebeia and identified by UV, IR, Mass, H-1 and C-13 NMR spectra. Their antioxidant activities were investigated individually and compared with alpha-tocopherol by the oxidative stability instrument (OSI) at 40 degrees C. The oils extracted from Styela clava and Ciona intestinalis Linnaeus with supercritical fluid (SCF) CO, and ethyl acetate, respectively, were used as substance oils, which were rich in polyunsaturated fatty acids (PUFA), especially in the long chain PUFA icosapentaenoic acid (EPA, 20:5n - 3) and docosahexaenoic acid (DHA, 22:6n - 3). beta-Sitosterol, 2 '-hydroxyl-5 '-methyoxybioctianin A and 6-methoxyluteolin-7-glycoside exhibited strong antioxidant activities, which increased markedly with increasing concentration, and even stronger than a-tocopherol. The results indicate that the components extracted from S. plebeia should preserve the quality of ascidian oil from ascidian oxidative deterioration. (c) 2005 Elsevier Ltd. All rights reserved.