Abstract: Objective: To screen the antibacterial fractions and constituents of Styela canopus Savigny. Method: The antibacterial activities of the ethanolic extract and organic fractions of S. canopus from the South China Sea was evaluated by diameter of antibacterial circle and the minimum bactericidal concentration ( MBC) , and the low- polar compounds in the petroleum ether fraction were also analyzed by gas chromatography- mass spectrometry ( GC-MS) . Results: The results showed that the antibacterial substances were mainly in the n- butanol and petroleum ether fraction, and 14 compounds were identified by GC- MS from petroleum ether fraction, most of which were lipids and sterols. Seven compounds were identified by GC- MS from the sterol component, and cholesterol was the dominant sterol. Four compounds were identified for the first time from S. subcrenata.Conclusion: The antibacterial activities of n- butanol and petroleum ether fraction from S. canopus were obvious, and cholesterol was the dominant sterol of petroleum ether fraction.