PAA-grafted MWNTs containing POSS (POSS/PAA-grafted MWNTs) were synthesized by the simple mixing of octa(3-aminopropyl)octasils-esquioxane (POSS-NH3+) and PAA-grafted MWNTs via ionic interactions. The spherical aggregates of Pd nanoparticles on the surface of POSS/PAA-grafted MWNTs (Pd-POSS/MWNTs) were produced with an average size of 10-20nm due to the effect of POSS-NH3+ used as a cubic linker physically attached to PAA-grafted MWNTs. The size of Pd-POSS/MWNTs was smaller than that of spherical aggregates of Pd nanoparticles prepared by only POSS-NH3+. The residual content of Pd-POSS/MWNTs is larger than that of POSS/PAA-grafted MWNTs because of the aggregates of Pd nanoparticles.