The gas-atomized Al-Si alloy powder with different particle sizes was subjected to isothermal annealing for understanding the effect of solidification rate on precipitation and growth Si crystals. The results show that Si precipitates grew more quickly in the small samples with a large solidification rate due to high interfacial energy. Moreover, these Si crystals had a tendency to form a quasi-spherical shape after annealing at a low temperature or for a short holding time. Coarsening of the Si precipitates during annealing was examined using a LSW equation. Thermal stability of the rapidly solidified alloy was significantly influenced by its original microstructure as a result of high solidification rate. Furthermore,more serious clustering of Si-Si phase was also observed in the small samples, attributed to the rapid coarsening of the Si phases. The gas-atomized Al-Si alloy powder with different particle sizes was subjected toothermal annealing for understanding the effect of solidification rate on precipitation and growth Si crystals. The results show that Si precipitates grew more quickly in the small samples with a large solidification rate due to high interfacial energy. Since these Si crystals had a tendency to form a quasi-spherical shape after annealing at a low temperature or for a short holding time. of the rapidly solidified alloys was significantly influenced by its original microstructure as a result of high solidification rate. Furthermore, more serious clustering of Si-Si phase was also observed in the small samples, attributed to the rapid coarsening of the Si phases.