Multiwalled carbon nanotubes (MWCNTs) were covalently functionalized with polyhedral oligomeric silsequioxane (POSS). The results of Fourier Transform Infrared Spectroscopy, Raman spectroscopy and Transmission Electron Microscopy indicated that POSS particles were grafted onto MWCNTs. The POSS content determined by thermo-gravimetric analysis (TGA) was estimated to be ∼25 wt%. A stable and superhydrophobic surface characteristic was observed for the film made of MWCNTs grafted with POSS (MWCNT-g-POSS) even after an exposure to a high-humidity environment for three weeks. The water contact angle of the sample was measured to be 160.5 ± 1.1°. Buckypapers were made from both pristine MWCNTs and chemically converted to MWCNT-g-POSS. The pore structures of the buckypapers were characterized by mercury intrusion porosimetry and scanning electron microscopy. The flame-retardant performance of the buckypaper-based composites was evaluated by TGA and microscale combustion calorimetry (MCC) test. The TGA test results indicated that the MWCNT-g-POSS dramatically increased the char residues of the composite. Approximately 72% reduction in peak heat release rate was achieved for the MWCNT-g-POSS /resin composite from the MCC testing. The fire-retardant mechanism was discussed. POLYM. ENG. SCI., 2013. © Society of Plastics Engineers