The invention belongs to the technical field of biomedicine and particularly relates to application of seaweed oligosaccharide in the preparation of an avian leucosis virus resistant preparation. seaweed oligosaccharide is prepared by degrading natural polysaccharides extracted from the macroalga Grateloupia filicina, Ulva lactuca, Sargassum fusiforme and other algae, has a wide source range, is simple to prepare, and has the advantages, as an antiviral preparation, such as naturalness, zero toxicity and environmental friendliness; in-vitro cell experiments prove that the seaweed oligosaccharide is capable of inhibiting the proliferation of avian leucosis virus, has significant antiviral effect, may be applied to livestock and poultry breeding as a novel antiviral preparation, and has high applicable value.