This paper describes the boundary element elastostatic analysis of a crack along the straight interface between two dissimilar materials. It is well known that the interface crack has an oscillation singularity at the crack tip which is quite different from a crack in homogeneous materials. Therefore, the definition of the stress intensity factor is not clarified yet and it is very difficult to analyze the interface crack by the numerical methods, such as FEM and BEM. We proposed a method to determine the stress intensity factors K₁ and K₂, for the interface crack by means of extrapolating the solutions at the points apart from the crack tip to avoid the oscillation singularity. This method can be widely applied to the BEM and also FEM analyses with any changes of the programmes. It is confirmed that the present results of the stress intensity factors for an interface crack in the infinite plate are completely consistent with the exact solutions. The stress intensity factors for various interface cracks in the finite plate and the adhesive joint are analyzed by the present method and BEM analyses, which is specially developed for this study.