In conventional solidification of multi-component mixtures, mushy zone appears between the pure solid and liquid regions and promotes the stable solidification by accepting the rejected solute regionally. From the standpoint that the fineness of inhomogeneity influences the mechanical properties in material processing, the way of linking macro-heat transfer and micro-solidificaion in the mushy zone was studied. Firstly, the crystal growth and its accompanying concentration field near the advancing front of mushy zone was observed precisely by using light absorption method. It was clarified that the mushy zone consisted of the leading front in which frame structure formed with accompanying concentration boundary layer, and the growing region where solidification proceeds by fattening of the crystals. Secondly, the crystal morphology was also investigated in relation with local quantity of state at the the leading front. The sidebranch evolution mechanism was studied in conjunction with interfacial instability due to constitutional supercooling and curvature supercooling around the primary arm surface. It was found that the primary arm spacing and secondary arm spacing are calculated from crystal growth velocity, local cooling velocity and crystal tip radius. Summarizing these results, micro-solidification process was quantitatively discussed in connection with macro-heat transfer.