Mn segregation at austenite/ferrite interface is studied in a Fe-C-Mn-Si alloy held at 656℃.Mn is partitioned during the growth of ferrite and as a result, a Mn pile-up exists in front of interface on the matrix side.An approach to evaluate Mn segregation quantitatively is developed by combining STEM raster window scanning and simulation of the interaction of the electron beam with the sample to subtract the contribution of Mn pile-up and obtain pure Mn segregation value.The evaluated maximum Mn interfacial segregation is in the order of a half-monolayer.