This paper deals with the X-ray diffraction characterisation of the mechanical behavior of a cast duplex stainless steel, containing 30% ferrite and 70% austenite. The structure of solidification leads a coarse grain material with grain size of the order of millimeters. The aim of the study is to identify the mechanical behavior for both phases by X-ray diffraction and to correlate it to the microstructure. The classical sin2w method for stress determination can not be applied to this material because of the large grains single size. The stresses are determined using a method resulting from an adaptation of the single crystal measurement method to large grains materials. So stress are determined using a method resulting Corn an adaptation of the single crystal measurement method to coarse grain materials. The measurement in each phase has successfully be applied to follow the stress state evolution during an in-situ tensile test. Three grains, with different crystallographic orientations were studied. For each one, the stress tensor was determined in the two phases under different macroscopic loading in elastic and plastic domains. For all grains, stress state in the ferritic phase is higher than the applied macroscopic stress and compared to the austenitic one where the stress is lower. This can be explained by ageing embrittlement of the ferrite which makes it much harder than the austenite. The important heterogeneity stress level is getting worse because of the crystallographic orientation of each grain. At each loading, micrographic observation are made to correlate the mechanical state determined by X-ray diffraction with the microstructure. Visible glides and cracks are noted and related to the stress state. This coupling of methods has been applied to identify the yield stress of each phase and the critical stress that leads to cracking of ferrite. The yield stresses so determined are in agreement with those deduced from the 8-28 peak broadening analysis.