Incompatibility between natural rubber (NR) and polypropylene (PP) can be overcome by the introduction of a compatibilizer that can induce interactions during blending. Compatibility is important as it may affect the morphology, mechanical and thermal properties of the blends. Among the commonly used compatibilizers is a liquid natural rubber (LNR). Apart from compatibility, mixing torque and curing are interrelated in determining the homogeneity of the TPNR blend. The LNR has the same microstructure with NR but with a short chain of polyisoprene (different in molecular weight, Mw). The LNR with some active terminals like –OH is expected to react with the plastic particles and thereby bond the plastic particles to the NR matrix. In this chapter, thermoplastic natural rubber TPNR reinforced with multi-walled carbon nanotube (MWCNTs) nanocomposites was prepared by the melt blending method. Using this method, MWCNTs will be dispersed homogeneously in the TPNR matrix in an attempt to increase the properties of these nanocomposites. The effect of MWCNTs on the mechanical and thermal properties of TPNR nanocomposites is reported in this chapter.