In　order　to　prepare　bismaleimide　(BMI)/montmorillonite　nanocomposites　with　high　performance,　Na-montmorillonite　(Na-MMT)　was　modified　with　allyl-tri-phenyl　phosphonium　bromide　(AP)　via　ion-exchange　method.　The　structures　and　properties　of　Na-MMT　and　AP-modified　MMT　were　characterized　by　FT-IR,　XRD,　TEM　and　TG.　The　results　show　that　AP　has　intercalated　into　the　layers　of　Na-MMT,　and　the　spacing　of　AP-modified　MMT　layers　increases　from　1.49　nm　to　1.85　nm.　Moreover,　AP-modified　MMT　possesses　good　thermo-stability　as　indicated　by　that　initial　thermal　decomposition　temperature　arrives　at　320C,　and　the　ion-exchange　rate　of　AP-modified　MMT　is　66.3%　according　to　TG　curves.