ObjectiveTo investigate the bioactive chemical constituents of gorgonian Muriceopsis flavida collected from the South China Sea. MethodsThe Et2O extract of the sample was purified by repeated column chromatographies on silica gel, Sephadex LH-20, and RP-HPLC. The structures of the obtained compounds were elucidated based on detailed spectroscopic analysis using mass spectrometry (MS) and nuclear magnetic resonance (NMR). The in vitro antimicrobial activities of the identified compounds were assessed by an agar diffusion test. ResultsFive 5α, 8α-epidioxy sterols were isolated from the Et2O extract (1-5),and their structures were determined as: (22E,24S)-5α,8α-epidioxy-24-methyl-cholesta-6,22-dien-3β-ol (1), (22E,24R)-5α,8α-epidioxy-24-methyl-cholesta-6,22-dien-3β-ol (2), (24R)-5α,8α-epidioxy-24-ethyl-cholesta-6-en-3β-ol (3), (22E)-5α,8α-epidioxy-cholest-6,22-dien-3β-ol (4), and 5α,8α-epidioxy-cholest-6-en-3β-ol (5). These compounds showed different degrees of antimicrobial activities in bioassay in vitro. ConclusionThe five compounds have been identified for the first time from the gorgonian Muriceopsis flavida. Compounds 2 shows a strong anti-algae effect and is worth further studying.