Abstract: The microstructure of Al-12.7%Si eutectic with addition of 0.1%Sr has been investigated across arrange of growth rate from 30 μm/s to 2 500μm/s with the aid of TEM. It has been shown that eutectic silicon phases contain high density of twins on two or more 111 systems and twin density and behavior are dependent on the growth rate. The preferred growth axis of silicon phases is in a <211 >irection and the microstructure of silicon phase can been seen as consisting of subgrains seperated by microtwins and/or stacking faults. Eutectic aluminum phases is multicrystal. There are no preferred matching relationship between eutectic aluminum and silicon phases.