The internal stress of epoxy resin generated during hardening process was analyzed by using simple viscoelastic model. The changes in the elastic modulus and volume of resin in the hardening process were measured. Their progresses were represented by the models with spring, dashpot, and shrinkage elements. The internal stresses and shrinkage behavior of resin were calculated by the finite element method and their results were compared with experimental results. Most of the internal stress was generated during the cooling process after curing. The effects of the internal stress on the strength of the adhesive bonded joints with epoxy resin were investigated. The joint strength was decreased by the internal stress. The effect was remarkable to the joint with short overlapped length.