Transient thermal stress distribution in an adhesive butt joint is considered. It is assumed that both the upper and lower end surfaces of the joint are maintained at different temperatures at a certain instant in time and that no heat transfers between the side surfaces of the joint and ambient air. In the analysis, two adherends were replaced with finite strips and unsteady temperature distribution in the joint was obtained theoretically. Then the transient thermal stress distribution in the joint was analyzed using a two-dimensional theory of elasticity. The effects of the ratios of the coefficient of thermal expansion and Young＇s modulus of the adherend to those of the adhesive on the thermal stress distribution were clarified from numerical calculations. Furthermore, the transient stress distribution in the adhesive was measured by a photoelastic experiment on a joint where the adhesive was modelled by an epoxy plate. The experimental results were consistent with the analytical results.