Bismaleimide-clay nanocomposites were synthesized by swelling two kinds of organophilic clays (OCLs) in allyl-compound modified bismaleimide (BMI) resins and subsequent thermal curing and characterized by DSC, Wide-angle X-ray diffraction (WAXD), Field emission SEM, TEM and Rheometer. The results indicated that the synthesis of modified BMI-clay nanocomposites, was determined by the factors including the preparation methodology, curing conditions, and nature of OCLs. Exfoliation of clay can be promoted by homogeniser and ultrasonication. Allyl-compound played a key role for the exfoliation of OCLs in modified BMI matrix as the pre-intercalation agent. It seems that the exfoliation should be carried out before gelation in order to obtain fully exfoliated structure in modified BMI matrix. The good combination of compatibility and acceleration effect on the intragallery polymerization are the favorable conditions to obtain exfoliated nanocomposites based on modified BMI matrix. The exfoliated structure favored the improvement in impact strength. (C) 2004 Elsevier Ltd. All rights reserved.