Ferritic oxide dispersion strengthened (ODS) alloy and stainless steel are attractive candidates for applications in the high temperature industries. Friction stir welding (FSW) is a very promising technique for the joining of both materials. Severe shear deformation and high heat input during FSW process can significantly change the microstructure and material property of the joints. The joint quality therefore plays a decisive role in material performance, life expectancy and cost. In this study, the different joints between ODS alloy and stainless steel were investigated in three different zones: the thermo-mechanically affected zone, the heat affected zone and the base material. Phase transformations and chemical reactions in the case of dissimilar welds were also studied. Electron backscattering diffraction (EBSD) was used to analyze the grain orientation, the grain boundary geometries and recrystallization behavior. Hardness changes within the welding zones and variation with grain boundary angle are discussed.