An object is to provide an epoxy-based adhesive having excellent properties such as tensile shear properties with a base material, curability, and heat resistance. An adhesive composition containing an epoxy resin composition (A), a curing catalyst (B), and a thixotropic agent (C), wherein the epoxy resin composition (A) contains a reaction product (c) of an epoxy resin (a) and a compound (b) having a phenolic hydroxy group, wherein an area ratio of the reaction product (c) is more than 2.0%, and 10% or smaller when total of areas of the epoxy resin (a), the compound (b) having a phenolic hydroxy group, and the reaction product (c) is taken as 100% in the area ratio measured by gel permeation chromatography.