The paramagnetic-antiferromagnetic transition and the gamma --> epsilon martensitic transformation of Fe-Mn (Mn 15-32 wt%) alloys have been investigated by resistivity, dilatometry and X-ray diffraction (XRD). The results show that paramagnetic-antiferromagnetic transition increases the resistivity and the volume of alloys, whereas the gamma --> epsilon martensitic transformation reduces the resistivity and volume of alloys. The A(f)(<)epsilon> that was determined by the dilatometric method is not the temperature that epsilon martensites in the Fe-Mn alloys have reverse transformed to austenites completely. Mn additions reduce M-s, increase T-N and the lattice parameter of austenite in the Fe-Mn alloys. Both the antiferromagnetic transition and the gamma --> epsilon martensitic transformation lead to an increase in the lattice parameter of austenite. The lattice parameters both above T-N and below T-N decrease linearly with temperature. The lattice parameter below M-s increases first and then decreases. Moreover, the alpha (110) and epsilon (002) atomic planes in the Fe-15Mn-0.15C alloy are separated into two peaks: 2 theta for epsilon>(*) over bar * (002) is 44.16 degrees, 2 theta for alpha>(*) over bar * (110) is 44.47 degrees.