The radial growth ofδ-phase in Fe-0.15%C-0.8%Mn steel during solidification was in-situ observed under a high-temperature confocal scanning laser microscope(HTCSLM).The correlation between radial growth rate of cylindrical solid and time in melt was investigated,and the expression was deduced.The results indicate that the radius of cellularδ-phase rapidly enlarges at the beginning,and then the enlargement amplitude gradually declines.The variation of radial growth rate vs time is the same for each cellularδ-phase,and the radial growth rate ofδ-phase rapidly declines to about 1.5μm/s within 10sat a cooling rate of 2.7K/min,after that the growth rate slowly falls.The experimental data of the radial growth rate of cellularδ-phase are consistent with the calculation results for Fe-0.15%C-0.8%Mn steel. The radial growth of δ-phase in Fe-0.15% C-0.8% Mn steel during solidification was in-observed observed in a high-temperature confocal scanning laser microscope (HTCSLM). The correlation between radial growth rate of cylindrical solid and time in melt was investigated, and the expression was deduced. Results indicate that the radius of cellular δ-phase is sharp enlarges at the beginning, and then the enlargement amplitude gradually declines. The variation of radial growth rate vs time is the same for each cellular δ-phase, and the radial growth rate of δ-phase rapidly declines to about 1.5 μm / s within 10 seconds of a cooling rate of 2.7 K / min, after that the growth rate of slow falls.The experimental data of the radial growth rate of cellular δ-phase are consistent with the calculation results for Fe-0.15% C-0.8% Mn steel.