In situ observation of growth process of high temperature phase in 0.15% C carbon steel during solidification concerned with using Confocal Scanning Laser Microscope (CSLM), the growth rate of -phase has been measured. The results indicate that high temperature -phase grows at cell crystal way when the cooling speed reaches 2°C/min in 0.15% C carbon steel. The -phase of round or oval cross-sectional shaped may grow stably. The growth rate of -phase is gradually getting slow along with increasing of curvature radius. The variation of growth speed tends to be similar with different solid-liquid interface shapes of -phase. The growth rate of concave solid-liquid interface is faster than that of convex solid-liquid interface for phase. The smaller radius of curvature of phase is, the faster the growth rate reaches.