The optimal induction heating conditions are proposed to obtain a uniform temperature, which affects a uniformity of solid fraction, throughout the billet during the thixoforming process. Heating method for providing a homogeneous temperature profile in overall cross section of the billet has been introduced. The optimal design of the induction coil has been identified as a function of coil size, ratio of semi-solid material diameter and coil one. The optimal coil design process of semi-solid aluminum alloy with d × l = 76 × 70 (㎜) to reduce the temperature gradient of the billet and to obtain the globular microstructure was theoretically proposed. The suitability of the coil design has been demonstrated by induction-heating experiments. The effect of the induction heating conditions on globular microstructure, grain growth and the solutions avoiding the coarsening phenomena has been discussed through the grain growth mechanism of Al-6%Si-3%Cu-0.3%Mg alloy. (Received January 5, 1999)