olyamidoamine (PAMAM) dendrimers up to the third generation (G) were grown onto the surface of functionalized multiwall carbon nanotubes (MWCNTs-NH₂) by a divergent method, the PAMAM-grafted-MWCNTs (PAMAM-g-MWCNTs) hybrid materials were obtained. Because of the surface modification of the multiwall carbon nanotubes with PAMAM dendrimers, these hybrid materials are not only soluble in aqueous medium but also are able to trap water soluble metal ions such as Pd²⁺ via complex formation of PAMAM dendrimer with metal ions. The reduction of trapped palladium ions in the dendritic shell of PAMAM-g-MWCNTs by sodium borohydride led to immobilized palladium nanoparticles on the surface of MWCNTs. Thus, palladium nanoparticles were immobilized by PAMAM-g-MWCNTs hybrid materials (PdNs-PAMAM-g-MWCNTs) and their application as a new nanocatalyst toward Heck reaction in different conditions was investigated. The G3 and G2 hybrid materials were found to be very active in cross-coupling reactions of aryl iodides, bromides and also chlorides with olefinic compounds in Heck reactions with short reaction time duration and high yields. The catalyst can be recycled several times without loss in activity.