The behaviour of boron segregation to grain boundaries in Fe-3%Si has been studied by means of particle tracking autoradiography. The results indicate that (i) the binding energy between boron atoms and grain boundaries is 55.7+/-1.7 kJ mol-1; (ii) in contrast to the nature of boron segregation in gamma-Fe, no observable non-equilibrium segregation of boron to grain boundaries exists in Fe-3%Si alloy during cooling and isothermal holding.