Strain-induced martensites in high manganese TRIP/TWIP steels were investigated by means of EBSD in the presence of thermal martensites and were analyzed in consideration of austenitic grain orientation.Before deformation the morphology of α′-M depended on the number of variants and growing period.Regardless of martensite morphologies and deformation, the K-S orientation relationships were always found. The 6 α′-M variants formedfrom a plate of ε-M were of 3 pairs of twins with a common axis <110>α parallel to the normal of {111}γ habit plane to minimize transformation resistance. When α′-M could form only by deformation, it nucleated at the intersection of ε-M variants and grew mainly in thick ε-M plates. Thick ε plates promoted significantly the α′-M and weakened the influence of grain orientations.Deformation twins promoted ε-M formation slightly and had no apparent effect on α′-M. Deformation increased the number of ε-M variants, but reduced that of α′-M variants.