The　AA3003　aluminium　alloy　was　deformed　by　isothermal　compression　in　the　deformation　temperature　range　300-500　degrees　C　at　a　strain　rate　of　0.1　s(-1)　with　a　Gleeble-1500　thermal　simulator.　The　microstructure　of　the　alloy　was　observed　by　OM　and　TEM,　and　the　hardness　was　measured　with　a　microhardness　tester.　The　results　show　that　the　flow　stress　decreases　with　an　increase　of　the　deformation　temperature.　The　dislocation　density　in　the　grain　is　large,　and　the　polygonal　structure　occurs　in　the　local　area　under　low-temperature　conditions.　When　the　temperature　reaches　400　degrees　C,　the　dislocation　density　decreases　gradually.　and　the　repetitive　polygonal　process　occurs.　The　deformation　mechanism　is　changed　from　dynamic　recovery　to　dynamic　recrystallization　(DRX).　The　DRX　volume　fraction　and　grain　size　increase　with　an　increase　of　the　deformation　temperature.　The　relationship　between　the　micro-Vickers　hardness　and　the　DRX　grain　size　of　the　alloy　after　hot　deformation　agrees　with　the　Hall-Petch　equation.　At　the　strain　rate　of　0.1　s(-1),　the　optimum　temperature　of　hot　deformation　for　the　alloy　is　about　400　degrees　C.