The　microstructures　and　mechanical　properties　of　eight　kinds　of　Fe-Cr-B-Al　alloys　containing　X　wt.%Al-0.35　wt.%C-10.0　wt.%Cr-1.4　wt.%B-0.6　wt.%Si-0.8　wt.%Mn　(X　=　0,　0.5,　1.0,　1.5,　2.0,　2.5,　3.0,　4.0)　were　studied　by　means　of　optical　microscopy　(OM),　scanning　electron　microscopy　(SEM),　X-ray　diffraction　(XRD),　Rockwell　hardness　and　Vickers　micro-hardness　testers.　The　results　indicate　that　the　as-cast　microstructure　of　aluminium-free　sample　consists　of　the　martensite,　austenite　and　eutectic　borocarbides,　and　the　eutectic　borocarbides　are　the　mixture　of　(Fe,　Cr)(2)B　and　(Cr,　Fe)(7)(C,　B)(3),　and　its　hardness　reaches　65　HRC.　When　a　small　amount　of　aluminium　element　(Al　＜=　1.0　wt.%)　is　added,　the　phase　composition　has　no　significant　change,　and　the　hardness　excels　65　HRC.　When　the　concentration　of　aluminium　reaches　1.5　wt.%,　the　matrix　of　Fe-Cr-B-Al　alloy　becomes　pearlite　and　delta-ferrite,　leading　to　a　sharply　decrease　of　the　hardness.　The　proportion　of　ferrite　goes　up　along　with　increasing　aluminium　concentration,　and　the　hardness　of　Fe-Cr-B-Al　alloy　has　slight　decrease.