Based　on　the　Fe-Cr-B　alloy,　the　Fe-12Cr-1.5B-xAl　(x　=　0,　2,　4,　6　and　8　wt%)　alloys　were　designed　by　adding　Al.　The　as-cast　microstructure　and　cyclic　oxidation　behavior　have　been　investigated　extensively　in　this　study.　The　results　reveal　that　the　as-cast　microstructure　of　Fe-Cr-B　alloy　consists　of　martensite　(bcc),　retained　austenite　(orthorhombic)　and　M-2(B,C)-bct,　M-7(C,B)(3)-hcp,　M-23(C,B)(6)-complex　fcc　boron-carbides,　gradually　changing　to　alpha-(Fe,Al,Cr)　solid　solution　(bcc),　M-2(B,C)-bct,　M-7(C,B)(3)-hcP,　M-23(C,B)(6)-complex　fcc　boron-carbides　and　Fe3Al　intermetallic　compound　with　the　increasing　of　Al　contents.　The　oxidation　kinetics　of　all　alloy　samples　follow　a　parabolic　oxidation　kinetic　law.　The　oxidation　rate　constant　k(p)　in　Al-free　Fe-Cr-B　alloy　is　nearly　four　times　of　that　in　Fe-Cr-B-8Al　alloy.　The　additions　of　Al　refine　the　grains　and　make　the　distribution　of　elements　more　uniform,　which　results　in　forming　a　continuous　and　dense　oxide　film　containing　Al2O3　oxide　with　excellent　fluidity　and　thermal　stability,　remarkably　enhancing　the　high　temperature　oxidation　resistance　of　Fe-Cr-B-Al　alloy.