Butt　joining　of　5052　aluminum　alloy　and　Q235　low　carbon　steel　was　achieved　using　laser　beam　welding　with　Sn30Zn　filler　wire.　The　weld　formation,　microstructures,　and　mechanical　property　were　investigated　with　varied　laser　power.　The　results　show　that　joining　of　5052　Al/Q235　steel　dissimilar　metals　in　a　butt　configuration　by　laser　beam　welding　with　Sn-30Zn　filler　wire　is　feasible.　The　solid　solution　interface　formed　at　the　aluminum　side　and　the　reaction　layer　formed　at　the　steel　side.　With　increasing　laser　power,　the　joining　mode　transformed　from　brazing　to　welding-brazing　due　to　the　melt　of　aluminum　alloy.　The　thickness　of　the　interfacial　intermetallic　compounds　(IMCs)　layer　was　also　increased　with　laser　power.　However,　when　the　laser　power　was　1200　W,　the　thickness　of　the　interfacial　IMCs　layer　sharply　decreased　due　to　the　detachment　of　the　IMCs　layer.　The　fracture　of　the　joint　occurred　at　the　steel　interface　and　partially　through　the　weld　seam　on　the　top　surface.　The　fracture　surface　was　characterized　by　both　brittle　and　ductile　fracture.　When　the　joints　were　obtained　at　the　laser　power　of　800　W　and　1200　W,　the　tensile　strength　reached　79　MPa　and　78　MPa,　respectively.　Furthermore,　the　formation　mechanism　of　microstructures　and　its　influence　on　mechanical　property　was　discussed.