The　effect　of　grain　size,　grain　orientation　and　precipitates　on　mechanical　properties　of　friction　stir　welded　5A06　aluminum　alloy　was　investigated　with　varying　rotation　speeds.　The　precipitation　behavior　and　grain　coarsening　were　discussed.　Recrystallization　occurred　in　the　weld　zones　and　recrystallization　texture　components　were　replaced　by　the　shear　texture　components　with　increased　rotation　speeds.　The　development　of　shear　texture,　precipitates　dissolution,　and　dislocations　pinned　by　precipitates　may　result　in　the　coarsening　of　the　grains　in　the　weld　zones　at　higher　rotation　speeds.　The　effect　of　grain　size　on　hardness　is　consistent　with　Hall-Petch　relationship.　All　the　welds　fractured　in　the　boundary　between　TMAZ　and　the　HAZ　at　the　AS　due　to　the　dislocations　pinned　by　the　precipitates　and　the　sharp　change　of　microstructure　at　the　AS.