Objective:　To　study　the　chemical　constituents　of　Gelidium　amansii　and　lay　a　foundation　for　the　research　and　development　of　functional　food　of　Gelidium　amansii.　Methods:　TLC　and　LC-MS　were　used　to　analyze　the　richness　of　chemical　components　in　the　ethanol　extract　of　Gelidium　amansii.　The　ethanol　extract　of　Gelidium　amansii　was　separated　and　purified　by　silica　gel　column　and　HPLC,　and　the　structure　of　compounds　were　determined　by　GC-MS,　NMR,　and　combined　with　the　data　reported　in　the　literature.　The　antioxidant　activity　of　some　compounds　was　determined.　Results:　TLC　and　LC-MS　analysis　showed　that　the　ethanol　extract　of　Gelidium　amansii　was　rich　in　secondary　metabolites,　and　it　was　likely　to　be　sterols.　29　compounds　(5　sterols)　were　identified　from　the　ethanol　extract　by　CC-MS.　Among　them,　palmitic　acid　(46.76%),　ethyl　palmitate　(13.82%),　cholesterol　(7.20%),　4,6-cholestadien-3beta　ol　(4.99%)　were　the　four　compounds　with　the　highest　content.　After　chromatographic　separation　and　NMR　identification,　9　compounds　were　obtained,　which　were　cholesterol　(1),　1,2-diol　phytoene　(2),　pagosterol　C　(3),　6-hydroxy-　cholest-4-en-3-one　(4),　cholest-5-en-7-one　(5),　cholest-5-ene-3β,　7α　diol　(6),　cholest-5-ene-3β,　7β　diol　(7),　cholest　-4-en-6-one　(8),　3-hydroxyethyl-2-methyl-maleimide　(9).　Compound　7　has　the　strongest　ability　to　scavenge　DPPH　and　ABTS　free　radical　with　IC50　values　of　0.18　mg/mL　and　12.2　μg/mL,　respectively.　Conclusion:　In　this　paper,　the　ethanol　extract　of　Gelidium　amansii　were　systematically　studied　for　the　first　time.　Compounds　3,　8　and　9　were　new　natural　products.　Some　sterols　showed　good　antioxidant　activity.　©　2024　Chinese　Institute　of　Food　Science　and　Technology.　All　rights　reserved.