Detailed description and exploitation of materials in nanoscale have become an obvious part of polymer-based composites with the speedy progression of nanotechnology. This review will focus on some of the nanocharacterization techniques that are most frequently used in current research of composite structures with an emphasis on the interface zone of natural fiber and polymer matrix. The fiber-polymer interface is a transition region, which extends nanometers to micrometers over which the mechanical and physical properties change from the bulk properties of fiber to the bulk properties of the polymer. Therefore, a better understanding of interfacial properties and characteristics will be helpful in estimating the ultimate properties of fiber-reinforced polymer composites. A number of case studies related to interface and its impact on the macroscale performance of the composites from the published literature are discussed.