The small-angle polarized neutron scattering (SAPNS) technique has been used to study a nuclear and magnetic homogeneity in the distribution of both substituent (Si, Cr, Ni) and interstitial (C, N) alloying elements on the mesoscopic range in Fe-Mn-based alloys with shape memory effect (SME). The four groups of alloys with various basic compositions: FeMn₁₈ (wt%), FeMn₂₀Si₆, FeMn₂₀Cr₉N_0.2 and FeMn₁₇Cr₉Ni₄Si₆ were investigated. It was found that the small-angle scattering of neutrons and depolarization on these alloys are very small altogether. The scattering did not exceed 1.5% from the incident beam and depolarization ∼2% for all samples. It means that these alloys are well nuclear and magnetically homogeneous on the scale of 10-1000Å. However, the difference in the homogeneity depending on the compositions still takes place. Thus, the adding of Si in FeMn₁₈ and FeMn₂₀Cr₉N_0.2 alloys improves the homogeneity pronouncedly. At once, the effect of the doping by C or N atoms on the homogeneity in FeMn₂₀Si₆ and FeMn₁₇Cr₉Ni₄Si₆ alloys is multivalued and depend on the presence of substitutional atoms (Ni and Cr). The capability of SAPNS as a method for the study of mesoscopic homogeneity in materials with SME and testing of the quality of their preparation is discussed.