An adhesive composition for forming an adhesive layer for temporarily fixing a substrate, such as a wafer, to a support when processing the substrate, the adhesive composition including a resin (A) produced by polymerizing a monomer component containing a cycloolefin-based monomer, at least one terpene-based resin, rosin-based resin, or petroleum resin (resin B), and an organic solvent capable of dissolving the resins (A) and (B). The resin (A) has a glass transition point of 60° C. or higher, the resin (B) has a softening point of 80 to 160° C. and a molecular weight of 300 to 3000, and the blending ratio of the resin (A) to the resin (B) is (A):(B)=80:20 to 55:45 (mass ratio).