The microstructural evolution of Fe–Mn–C austenitic steels, which exhibit outstanding high-ductile deformation in their plastic regions, was characterized by line-profile and texture analyses. The convolutional multiple whole profile fitting procedure was used for a line-profile analysis of 2θ−θ diffraction data to evaluate variations of crystallite size, dislocation density, and dislocation arrangement. A substantial refinement of the crystallite size proceeded at an early deformation stage. In addition, the dislocation density increased with an increase in the tensile strain. Texture evolution was characterized by the analysis of orientation distribution functions. Three texture components grew with an increase in the tensile strain. According to the pole figure describing the full width at half maximum (FWHM) distribution of the 220 reflection, the nontextured grains had more microstructural defects than the textured grains. To evaluate the microstructural defects in detail, the 220 reflection observed at each texture orientation was analyzed by the single-line-profile method. The crystallite size and dislocation density were almost comparable, irrespective of the kind of texture component. The crystallite size of the nontextured grains was also comparable to that of the textured grains, whereas the nontextured grains had a dislocation density several times that of the textured grains.