The relationship between microscopically localized stress (microscopic stress) in a polycrystalline material and initiation of intergranular stress corrosion cracking (IGSCC) was studied by combining experiments and finite element computations. The microscopic stress distribution in a small tensile test piece of Alloy 600MA under tension load was evaluated by energy-dispersive X-ray diffraction with white X-ray micro beam. Stress estimation by crystal plasticity finite element method (CPFEM) was carried out for a model constructed from the microstructure of the test piece used for the measurement. In the computation result, the deformation showed relatively good agreement with the observed result, while microscopic stress showed significant gap with the observed values. This gap is due to the limitations of both the computational and the experimental methods. SCC tests of nickel-base Alloy 600MA and Alloy X-750 were conducted in potassium tetrathionate solution and simulated PWR primary water. The microscopic stress state around the cracked locations was estimated by finite element computation using polycrystalline aggregate model to assess the condition of crack initiation. It was concluded that localized high stress significantly contributed to an initiation of IGSCC, although it was not the only dominant factor. It is suggested that other factors like oxidation, and transport phenomenon of atom or chemical species in metal could have an effect comparable to that of microscopic stress.