Dissimilar　Al/steel　butt　joints　of　6.0　mm　thick　plates　have　been　achieved　using　fiber　laser　keyhole　welding　autogenously.　The　cross　sections,　interface　microstructures,　hardness　and　tensile　properties　of　Al/steel　butt　joints　obtained　under　different　travel　speeds　and　laser　beam　offsets　were　investigated.　The　phase　morphology　and　thickness　of　the　intermetallic　compound　(IMC)　layers　at　the　interface　were　analyzed　by　scanning　electronic　microscopes　(SEM)　using　the　energy-dispersive　spectrometry　(EDS)　and　electron　back-scattered　diffraction　(EBSD)　techniques.　The　results　show　that　travel　speeds　and　laser　beam　offsets　are　of　considerable　importance　for　the　weld　shape,　morphology　and　thickness　of　IMC　layers,　and　ultimate　tensile　strength　(UTS)　of　Al/steel　butt　joints.　This　proves　that　the　IMC　layers　consist　of　Fe2Al5　phases　and　Fe4Al13　phases　by　EBSD　phase　mapping.　Increasing　laser　beam　offsets　from　0.3　mm　to　0.7　mm　significantly　decreases　the　quantity　of　Fe4Al13　phases　and　the　thickness　of　Fe2Al5　layers　at　the　interface.　During　tensile　processing,　the　Fe2Al5　layer　with　the　weakest　bonding　strength　is　the　most　brittle　region　at　the　interface.　However,　an　intergranular　fracture　that　occurred　at　Fe2Al5　layers　leads　to　a　relatively　high　UTS　of　Al/steel　butt　joints.