Provided is an adhesive composition containing component (A) (a modified polyolefin-based resin) and component (B) (a polyfunctional epoxy compound), wherein as a result of measuring a storage elastic modulus of a solid content, a storage elastic modulus at 23° C. is 0.1 to 600 MPa, and a storage elastic modulus at 80° C. is 0.1 MPa or lower. Also provided are: a sealing sheet having an adhesive layer formed using the adhesive composition, and a sealed body comprising a seal object that is sealed with the sealing sheet. The adhesive composition is easy to form into a sheet and excellent in unevenness followability. The sealing sheet has an adhesive layer which is formed of this adhesive composition and is excellent in unevenness followability, and a sealed body has a seal object sealed with the sealing sheet.