Epoxy resin, epoxy resin composition, epoxy resin cured product, and composite material

Provided is an epoxy resin which contains: a first epoxy compound having a mesogen structure; and a second epoxy compound having two or more mesogen structures identical to the mesogen structure of the first epoxy compound, wherein the proportion of the first epoxy compound as measured by liquid chromatography is 50% or less of the total epoxy resin.