Preparation　and　characterization　of　bismaleimides　(BMI)/montmorillonite　(MMT)　nanocomposites　was　investigated　in　this　paper.　Na-montmorillonite　was　modified　with　allyl-tri-phenyl　phosphonium　bromide　(AP)　by　cation-exchange　method　to　obtain　organic　MMT　(OMMT),　and　diallylbisphenol　A　was　used　as　modifier　for　BMI　resin.　The　nanocomposites　were　prepared　via　in　situ　polymerization,　and　the　properties　of　the　nanocomposites　were　characterized　by　FT-IR,　WAXD,　TEM,　TGA.　The　results　show　that　AP　reacts　with　BMI　to　form　covalent　bond　due　to　the　active　group　of　allyl,　favoring　high　interfacial　bonding　performance　between　MMT　and　matrix　resin.　The　exfoliated　nanocomposites　can　be　obtained,　due　to　the　relatively　complete　intercalation　of　matrix　resin　to　the　OMMT　when　the　OMMT　content　is　kept　low.　Moreover,　the　thermal　stability　of　the　nanocomposites　is　improved,　the　initial　decomposition　temperature　of　which　increases　from　418.2C　to　439.6C.