Multiwalled carbon nanotubes (MWNTs) functionalized with hyperbranched aliphatic polyamide (HAP) were prepared by polycondensation using 3-(2-aminoethylamino)propanoic acid methyl ester as monomer. The effects of HAP functionalized MWNTs (MWNT-HAP) on the properties of bismaleimide (BMI) resin were investigated. Nanocomposites based on BMI resin and different content of MWNTs were prepared. The properties of nanocomposites were characterized by TGA, DMA, flexural and impact tests. Because of the magnification of functional groups and the higher interfacial interaction between MWNT-HAP and BMI resin, the improvement of the mechanical and thermal properties of MWNT-HAP/BMI nanocomposites was more remarkable than nanocomposites containing pristine MWNTs.