The objective of this chapter is to use the spectroscopy techniques such as UV-vis spectroscopy, Fourier-Infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), Raman spectroscopy, electron spin resonance (ESR) for analysing in the chemical and physical interaction, degradation and blend composition as well as dynamic properties of polymer blends based on natural rubber (NR) or its derivative with another polymer. For example, the UV bands of epoxidized natural rubber (ENR) and poly(ethylene-co-acrylic acid) (PEA) shifts than that polymer alone were confirmed by UV-vis spectroscopy due to its etherification reaction between OH groups formed in situ during melt blending ENR and –COOH groups of PEA. The ester moiety in NR/polystyrene foam waste (PSf) containing maleic anhydride (MA) in presence of ester was confirmed by ATR-FTIR. In case of NMR, it seems to be highly suitable technique for characterizing the chemical interaction and degradation of between NR and another polymer. The interaction between the abnormal groups such as hydroxyl function from ENR is found, resulting in improving the compatibility of the blends, then increasing toughness. The interaction of polymer blend comprising polyvinylidene fluoride (PVDF) and latex of NR was confirmed by Raman spectroscopy. Finally, ESR was used to identify the mechanism in interaction of polypropylene (PP)/ENR blends.