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 GC-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.