Island-nanomatrix structure, discovered as a nanostructure inherent to natural rubber, is one of the essential key-factors in elucidating the reason why natural rubber possesses better balanced mechanical properties required for a raw rubber. It is important to understand how the island-nanomatrix structure is formed, what roles it plays, and how it affects mechanical properties. In this review article, first, a formation of the island-nanomatrix structure is elucidated in relation to a biosynthesis pathway of natural rubber. Effects of the island-nanomatrix structure on the mechanical properties, oxidative degradation and vulcanization are explained to be due to proteins present in natural rubber, which are major components of the nanomatrix. Second, the island-nanomatrix structure is divided into constitutive units to figure out how it is constructed. A strategy to prepare natural rubber with a model island-nanomatrix structure is described in a view point of a reconstruction of the constitutive units. Furthermore, the effect of the island- nanomatrix structure on the mechanical properties is elucidated with natural rubber with the model island-nanomatrix structure. The island-nanomatrix structure is proved to play an important role in the mechanical properties of natural rubber.