Abstract: At the grain boundaries of Al-0.35%Si alloy samples which are treated at high solution treatment temperature followed by uniform cooling, the Si-rich precipitates could be found, and the relative amounts of precipitates increased with the increasing of solution treatment temperature. For the samples which are firstly treated at higher solution temperatures and then treated at lower solution temperature followed by uniform cooling, the amount of precipitates is the maxinum for 25min. For the sample treated for 25min at lower temperature followed by water quench, precipitates which are larger than 1μm could be observed at grain boundaries. The above results show that non-equilibrium segregation of silicon exists at the grain boundary of aluminum.